Rovibrational Analysis Research Articles

Microwave Spectroscopy of Chiral Astrochemical Candidate Vinyloxirane: The Missing Gauche Conformer.

The recent detection of a chiral molecule, propylene oxide, in the interstellar medium provides impetus for investigation of related analogues as candidates for discovery of a second chiral species. Vinyloxirane (VO) shares many of the characteristics of propylene oxide that favored its remote detection such as modest size, appreciable dipole moment and modest adsorption to water ice. The microwave spectrum of vinyloxirane at room temperature has been studied in the 18 - 26 GHz region. Rotational transitions of the previously undetected gauche-1 conformer have been assigned and fitted. The quantum number range of anti conformer transitions has been greatly expanded, providing improved molecular constants. Vibrational satellite transitions were assigned and fitted for the lowest frequency ν27 torsion mode, for 2ν27, and for the ν26 C=CC bend of anti VO, along with ν27 satellites of gauche-1. The rovibrational analyses were assisted by anharmonic vibrational calculations at B3LYP-D3/aug-cc-PVTZ, B2PLYPD3/cc-pVTZ, and DSDPBEP86/cc-pVTZ levels. Experimental peak intensities provide a population ratio Ngauche-1/Nanti of 0.36 ± 0.06, corresponding to a Gibbs free energy difference of 2.5 ± 0.4 kJ mol-1 in favor of the anti conformer, in agreement with the density functional theory results. In the gauche-1 conformer, the torsional angle between vinyl group and oxirane ring, τC=CCM, is optimized at -35° to favor an intramolecular CvinylH11...O interaction. The gauche-2 conformer with τC=CCM of + 74° suffers from CvinylH11...HCcyclopropyl repulsion so that it is calculated to be 8-9 kJ mol-1 higher than gauche-1. Reinterpretation of earlier Raman spectra suggests that the gauche-2 conformer had not been observed as reported.

High resolution far-infrared synchrotron spectroscopy of 2-furfural conformers: Fundamental and hot bands.

In the continuity of a previous jet-cooled rovibrational study of trans and cis conformers of 2-furfural in the mid-infrared region (700-1750cm-1) [Chawananon et al., Molecules 28 (10), 4165 (2023)], the present work investigates the far-infrared spectroscopy of 2-furfural using a long path absorption cell coupled to a high-resolution Fourier transform spectrometer and synchrotron radiation at the AILES beamline of the SOLEIL synchrotron. Guided by anharmonic calculations, vibrational energy levels and excited-state rotational constants are sufficiently predictive for a complete assignment of all fundamental and combination bands up to 700cm-1, as well as the rovibrational analysis of 4 (1) low-frequency modes of trans-(cis-)2-furfural. A global rovibrational simulation, including far-infrared rovibrational lines and microwave and millimeter-wave rotational lines assigned in a previous study [Motiyenko et al., J. Mol. Spectrosc., 244, 9 (2007)] provides a reliable set of ground- and excited-state rotational parameters involving ring torsion, bending, and ring puckering modes of 2-furfural. In a second step, a rovibrational analysis of several hot band sequences, mainly involving the lowest frequency ring CHO torsion mode, is carried out. Reliable values of some anharmonic coefficients are obtained experimentally and could serve as a benchmark for validating advanced anharmonic calculations related to these large amplitude motions of flexible molecules.

Rovibrational analysis of AlCO3, OAlO2, and HOAlO2 for possible atmospheric detection.

The lack of observational data for the AlO molecule in the mesosphere/lower thermosphere may be due to ablated aluminum reacting quickly to form other species. Previously proposed reaction pathways show that aluminum could be ablated in the atmosphere from meteoritic activity, but there currently exist very limited spectroscopic data on the intermediates in these reactions, limiting the possible detection of said molecules. As such, rovibrational spectroscopic data are computed herein using quartic force field methodology at four different levels of theory for the neutral intermediates AlCO3, OAlO2, and HOAlO2. Each molecule exhibits multiple vibrational modes with large vibrational transition intensities. For instance, the C-O stretch (ν1) in AlCO3 has a harmonic intensity of 536 km mol-1, the Al-O stretch (ν2) in OAlO2 has an intensity of 678 km mol-1, and the out-of-plane torsion (ν9) in HOAlO2 has an intensity of 158 km mol-1. All three molecules have exceptionally large dipole moments of 6.27, 4.21, and 5.04D, respectively. These properties indicate that all three molecules are good candidates for potential atmospheric observation utilizing vibrational and/or rotational spectroscopic techniques.

Reaction Pathway and Rovibrational Analysis of Aluminum Nitride Species as Potential Dust Grain Nucleation Agents

A dust nucleating agent may be present in interstellar or circumstellar media that has gone seemingly undetected and unstudied for decades. Some analyses of the Murchison CM2 meteorite suggest that at least some of the aluminum present within condensed as aluminum nitrides instead of the long-studied, but heretofore undetected suite of aluminum oxides. The present theoretical study utilizes explicitly correlated coupled cluster theory and density functional theory to provide a formation pathway from alane (AlH3) and ammonia to the cyclic structure Al2N2H4, which has the proper Al/N ratio expected of bulk aluminum nitrides. Novel rovibrational spectroscopic constants are computed for alane and the first two formed structures, AlNH6 and AlNH4, along the reaction pathway for use as reference in possible laboratory or observational studies. The ν 8 bending frequency for AlNH6 at 755.7 cm−1 (13.23 μm) presents a vibrational transition intensity of 515 km mol−1, more intense than the antisymmetric C−O stretch of carbon dioxide, and contains a dipole moment of 5.40 D, which is ∼3× larger than that of water. Thus, the present reaction pathway and rovibrational spectroscopic analysis may potentially assist in the astrophysical detection of novel, inorganic species which may be indicative of larger dust grain nucleation.

Vibrational bands of formaldoxime isotopologue 13CD2NOH in the 280–4000 cm−1 region and rovibrational analysis of its [formula omitted] band by Fourier transform infrared (FTIR) spectroscopy

A total of 11 fundamental and 3 overtone bands of the formaldoxime isotopologue 13CD2NOH were identified using its Fourier transform infrared (FTIR) spectra which were recorded with a low resolution (0.50 cm−1) in the 500–4000 cm−1 region, and high resolution (0.00096 cm−1) in the 280–500 cm−1 region. Their relative infrared (IR) band intensities were also measured. Furthermore, a rovibrational analysis of the IR transitions of the ν12 band of 13CD2NOH was carried out using its high-resolution FTIR spectrum which was recorded at the Australian Synchrotron. A total of 1077 IR transitions of the C-type ν12 band were assigned and fitted using the Watson's A-reduced Hamiltonian in the Ir representation to derive its band center and the v12 = 1 state rovibrational constants up to all 5 quartic centrifugal distortion terms for the first time, with a root-mean-square (rms) deviation of 0.00044 cm−1. The band center of the ν12 band of 13CD2NOH were found to be 391.054446(36) cm−1. The ground state rovibrational constants up to all 5 quartic terms were determined for the first time by fitting 407 ground state combination differences (GSCDs) derived from the assigned IR transitions of the ν12 band of 13CD2NOH of this work. The rms deviation of the GSCD fit was 0.00040 cm−1. Additionally, all 3 rotational constants and 5 quartic centrifugal distortion terms of the ground state and 3 rotational constants of the v12 = 1 state of 13CD2NOH were computed from theoretical anharmonic calculations at two different levels of theory, B3LYP and MP2 with the cc-pVTZ basis set, for comparison with the experimental results. Close agreement was found for the calculated and experimental rovibrational constants of 13CD2NOH for both ground and v12 = 1 states. The vibrational anharmonic frequencies of the 12 fundamental bands of 13CD2NOH in the 280–4000 cm−1 region, and their IR band intensities were also calculated using B3LYP and MP2 with the cc-pVTZ basis set, and they were compared with the respective experimental data. Finally, the ground state rotational constants and the band center of the ν12 band of the cis conformer of 13CD2NOH were calculated and compared with those of the trans conformer of this work.

High-resolution infrared spectra and rovibrational analysis of the ν12 band of propylene oxide.

The high-resolution infrared spectrum of the fundamental band ν12 (ring breathing) of the chiral molecule propylene oxide (CH3CHCH2O) was recorded at room temperature and under jet-cooled conditions using a quantum cascade laser at 8 μm. The observed lines with quantum numbers J ≤ 55 and Ka ≤ 21 were assigned to strong b- and c-type bands, and some low J transitions were classified as weak a-type transitions. The lines were fitted using a Watsons A-reduced Hamiltonian in the Ir representation. From the rovibrational analysis the band origin as well as the rotational constants and four quartic centrifugal distortion constants were derived.

High resolution infrared spectra of neopentane: Rovibrational analysis of bands at 8.3–6.4 μm

High resolution (0.0014 cm−1) infrared spectra of neopentane (2,2-dimethylpropane) have been recorded at 203 K at the Canadian Light Source. Spectra were recorded in the infrared (8.3–6.4 μm) with 8 m of optical path. Neopentane is a spherical top molecule with Td (tetrahedral) symmetry. A low temperature is favorable for a detailed rotational analysis of its fundamental bands.This study focuses on the analysis of 3 band systems of neopentane. The first system is a dyad consisting of a ν15 fundamental band and a ν7 + ν19 combination band located at 1472.5 and 1489 cm−1, respectively. The second system is a ν16 fundamental band located at 1369.4 cm−1 with uncertain band origin. The third band system is a dyad of a ν17 fundamental and a ν8 + ν18 combination band. Only the ν17 fundamental band was analyzed in this last system due to the weaker intensity of the combination band. For all spectral simulations and calculations an ‘XTDS’ program based on tensorial formalism by the Dijon molecular spectroscopy group was used. A subprogram ‘SPVIEW’, paired with XTDS, was used for spectral assignment.

Comparative line position and line strength analysis of the [formula omitted] dyad of [formula omitted] and [formula omitted

A highly accurate ro-vibrational analysis of FTIR spectra (line positions of 13CD4 and line strengths of both the 12CD4 and 13CD4 species) is presented. The high-resolution infrared spectra of both molecules were measured with a Bruker IFS125 HR Fourier transform infrared spectrometer at an optical resolution of 0.003 cm−1 and analyzed in the regions of 800–1400 cm−1 where the ν2/ν4 dyad is located. The number of 901 transitions with Jmax=23 were assigned to the ν4 and ν2 bands of 13CD4 (this number is about 5.3 times higher in comparison with the number of known assigned transitions for 13CD4). The weighted fit of experimental line positions was made using the Hamiltonian model which takes into account the resonance interactions between the (0001,F2) and (0100,E) vibrational states. As a result, set of 18 fitted parameters of the (0001,F2)/(0100,E) vibrational states of 13CD4 was determined which reproduce the initial 901 experimental ro–vibrational line positions with the drms=2.59×10−4 cm−1, which is close to the experimental uncertainty of the recorded spectra and about 1330 times better in comparison with the reproduction of the same line position values by the use of parameters from Loëte et al. (1983). The analysis of 1557 experimental lines of the dyad of 12CD4 and 131 lines of the dyad of 13CD4 was fulfilled with the Hartmann–Tran profile to simulate the measured line shape and to determine experimental line intensities. Sets of 6/1 varied effective dipole moment parameters of 12CD4/13CD4 are determined which reproduce the initial 1557/131 line strengths with the drms=4.80% and 4.21%. Lists of the assigned line positions and strengths in the studied region are presented as the Supplementary data to this paper.

Fourier transform infrared (FTIR) spectroscopy of formaldoxime isotopologue 12CD2NOH in the 300–3700 cm−1 region and its ν12 and ν9 bands: Vibrational and rovibrational analyses

The Fourier transform infrared (FTIR) spectrum of the formaldoxime isotopologue 12CD2NOH was recorded in the 500–3700 cm−1 region with a resolution of 0.50 cm−1 to identify its fundamental, overtone and combination bands and to measure their relative infrared (IR) band intensities. Furthermore, the high-resolution (0.00096 cm−1) FTIR spectrum of ν12 and ν9 bands of 12CD2NOH was recorded in Australian Synchrotron in the 300–510 cm−1 region for a rovibrational analysis. A total of 1060 IR transitions of the C-type ν12 band were fitted using the Watson's A-reduced Hamiltonian in the Ir representation with a root-mean-square (rms) deviation of 0.000524 cm−1. From the rovibrational analysis, the v12 = 1 state rovibrational constants up to all 5 quartic centrifugal distortion terms were derived for the first time. The band center of the ν12 band of 12CD2NOH was found to be 391.214740(46) cm−1. The ground state rovibrational constants up to all 5 quartic terms were determined for the first time by the fitting of 423 ground state combination differences (GSCDs) derived from the IR transitions of the ν12 band of 12CD2NOH of this work. The rms deviation of the GSCD fit was 0.000473 cm−1 using the Watson’s A-reduced Hamiltonian in the Ir representation. Furthermore, a total of 724 IR transitions of the predominantly B-type ν9 band of 12CD2NOH were fitted with a rms deviation of 0.000360 cm−1 to derive the band center at 465.151277(39) cm−1 and rovibrational constants of the v9 = 1 state up to 4 quartic terms for the first time. Additionally, all 3 rotational constants and 5 quartic centrifugal distortion terms of the ground state and 3 rotational constants of the v12 = 1 and v9 = 1 states of 12CD2NOH were computed from theoretical anharmonic calculations at 2 different levels of theory, B3LYP and MP2 with the cc-pVTZ basis set, for comparison with the experimental results. Close agreement was found for the calculated and experimental rotational constants of 12CD2NOH for the ground, v12 = 1 and v9 = 1 states. The vibrational frequencies (cm−1) of 12 fundamental bands of 12CD2NOH in the 300–3700 cm−1 region, and their IR band intensities (km/mol) were also calculated using B3LYP and MP2 with the cc-pVTZ basis set, and they were compared with the respective experimental data.

Hyperfine-resolved spectra of HDS together with a global ro-vibrational analysis.

Despite their chemical simplicity, the spectroscopic investigation of light hydrides, such as hydrogen sulfide, is challenging due to strong hyperfine interactions and/or anomalous centrifugal-distortion effects. Several hydrides have already been detected in the interstellar medium, and the list includes H2S and some of its isotopologues. Astronomical observation of isotopic species and, in particular, those bearing deuterium is important to gain insights into the evolutionary stage of astronomical objects and to shed light on interstellar chemistry. These observations require a very accurate knowledge of the rotational spectrum, which is so far limited for mono-deuterated hydrogen sulfide, HDS. To fill this gap, high-level quantum-chemical calculations and sub-Doppler measurements have been combined for the investigation of the hyperfine structure of the rotational spectrum in the millimeter- and submillimeter-wave region. In addition to the determination of accurate hyperfine parameters, these new measurements together with the available literature data allowed us to extend the centrifugal analysis using a Watson-type Hamiltonian and a Hamiltonian-independent approach based on the Measured Active Ro-Vibrational Energy Levels (MARVEL) procedure. The present study thus permits to model the rotational spectrum of HDS from the microwave to far-infrared region with great accuracy, thereby accounting for the effect of the electric and magnetic interactions due to the deuterium and hydrogen nuclei.

Gas-phase formation and spectroscopic characterization of the disubstituted cyclopropenylidenes c-C3(C2H)2, c-C3(CN)2, and c-C3(C2H)(CN)

Aims. The detection of c-C3HC2H and possible future detection of c-C3HCN provide new molecules for reaction chemistry in the dense interstellar medium (ISM) where R-C2H and R-CN species are prevalent. Determination of chemically viable c-C3HC2H and c-C3HCN derivatives and their prominent spectral features can accelerate potential astrophysical detection of this chemical family. This work characterizes three such derivatives: c-C3(C2H)2, c-C3(CN)2, and c-C3(C2H)(CN). Methods. Interstellar reaction pathways of small carbonaceous species are well replicated through quantum chemical means. Highly accurate cc-pVXZ-F12/CCSD(T)-F12 (X = D,T) calculations generate the energetics of chemical formation pathways as well as the basis for quartic force field and second-order vibrational perturbation theory rovibrational analysis of the vibrational frequencies and rotational constants of the molecules under study. Results. The formation of c-C3(C2H)2 is as thermodynamically and, likely, as stepwise favorable as the formation of c-C3HC2H, rendering its detectability to be mostly dependent on the concentrations of the reactants. Both c-C3(C2H)2 and c-C3(C2H)(CN) will be detectable through radioastronomical observation with large dipole moments of 2.84 D and 4.26 D, respectively, while c-C3(CN)2 has an exceedingly small and likely unobservable dipole moment of 0.08 D. The most intense frequency for c-C3(C2H)2 is v2 at 3316.9 cm–1 (3.01 μm), with an intensity of 140 km mol–1. The mixed-substituent molecule c-C3(C2H)(CN) has one frequency with a large intensity, v1, at 3321.0 cm–1 (3.01 μm), with an intensity of 82 km mol–1. The molecule c-C3(CN)2 lacks intense vibrational frequencies within the range that current instrumentation can readily observe. Conclusions. Both c-C3(C2H)2 and c-C3(C2H)(CN) are viable candidates for astrophysical observation, with favorable reaction profiles and spectral data produced herein, but c-C3(CN)2 will not be directly observable through any currently available remote sensing means, even if it forms in large abundances.

Formation and detection of metastable formic acid in a supersonic expansion: High resolution infrared spectroscopy of the jet-cooled cis-HCOOH conformer.

High-resolution direct absorption infrared spectra of metastable cis-formic acid (HCOOH) trapped in a cis-well resonance behind a 15 kcal/mol barrier are reported for the first time, with the energetically unstable conformer produced in a supersonic slit plasma expansion of trans-formic acid/H2 mixtures. We present a detailed high-resolution rovibrational analysis for cis-formic acid species in the OH stretch (ν1) fundamental, providing first precision vibrational band origin, rotational constants, and term values, which in conjunction with ab initio calculations at the couple-cluster with single, double, and perturbative triple [CCSD(T)]/ANOn (n = 0, 1, 2) level support the experimental assignments and establish critical points on the potential energy surface for internal rotor trans-to-cis isomerization. Relative intensities for a- and b-type transitions observed in the spectra permit the transition dipole moment components to be determined in the body fixed frame and prove to be in good agreement with ab initio CCSD(T) theoretical estimates but in poor agreement with simple bond-dipole predictions. The observed signal dependence on H2 in the discharge suggests the presence of a novel H atom radical chemical mechanism for strongly endothermic "up-hill" internal rotor isomerization between trans- and cis-formic acid conformers.

Quantum chemical rovibrational analysis of aminoborane and its isotopologues.

Aminoborane, H2 NBH2 and its isotopologues, H2 N10 BH2 , D2 NBD2 , and D2 N10 BD2 , have been studied by high-level ab initio methods. All calculations rely on multidimensional potential energy surfaces and dipole moment surfaces including high-order mode coupling terms, which have been obtained from electronic structure calculations at the level of explicitly correlated coupled-cluster theory, CCSD(T)-F12, or the distinguishable cluster approximation, DCSD. Subsequent vibrational structure calculations based on second-order vibrational perturbation theory, VPT2, and vibrational configuration interaction theory, VCI, were used to determine rotational constants, centrifugal distortion constants, vibrationally averaged geometrical parameters and (an)harmonic vibrational frequencies. The impact of core-correlation effects is discussed in detail. Rovibrational VCI calculations were used to simulate the gas phase spectra of these species and an in-depth analysis of the ν7 band of aminoborane is provided. Color-coding is used to reveal the identity of the individual progressions of the rovibrational transitions for this particular mode.

Fourier transform infrared (FTIR) spectrum (250–3800 cm−1) of formaldoxime-13C (13CH2NOH) and rovibrational analysis of its [formula omitted] band

The Fourier transform infrared (FTIR) spectrum of formaldoxime-13C (13CH2NOH) was recorded in the 600–3800 cm−1 region with a resolution of 0.50 cm−1 to identify its fundamental and overtone bands and to measure their relative infrared band intensities. Furthermore, the high-resolution (0.00096 cm−1) FTIR spectrum of the ν12 band of 13CH2NOH was recorded at the Australian Synchrotron in the 250–600 cm−1 region for a rovibrational analysis. A total of 1506 infrared (IR) transitions of the C-type ν12 band were fitted using the Watson's A-reduced and S-reduced Hamiltonians in the Ir representation with a root-mean-square (rms) deviation of 0.000364 cm−1 for both fits. From the rovibrational analysis, the v12 = 1 state rovibrational constants up to one sextic centrifugal distortion term were derived for the first time. The band center of the ν12 band of 13CH2NOH were found to be 397.365846(32) cm−1 in the A-reduced Hamiltonian. The ground state rovibrational constants up to one sextic term were improved with higher accuracy by fitting 1374 ground state combination differences (GSCDs) derived from the IR transitions of the ν8 and ν12 bands of 13CH2NOH, together with two previously reported microwave frequencies. Furthermore, a comparison of the experimental vibrational frequencies, IR band intensities, rovibrational constants (v12 = 1 and ground states) of 13CH2NOH and those derived from theoretical calculations at two levels of theory: B3LYP and MP2 with cc-pVTZ basis set were made. Close agreement was found for the calculated and experimental rovibrational constants of 13CH2NOH for both ground and v12 = 1 states.

Rovibrational analysis of the [formula omitted] and 2[formula omitted][formula omitted] bands of deuterated formaldoxime (CH2NOD) by high-resolution synchrotron FTIR spectroscopy

The high-resolution Fourier transform infrared (FTIR) spectrum of the ν12 band and its hot band 2ν12-ν12 of deuterated formaldoxime (CH2NOD) was recorded at the far-IR beamline of Australian Synchrotron with an unapodized resolution of 0.00096 cm−1 in the 230–350 cm−1 region. A total of 1456 infrared transitions of the ν12 band was fitted using the Watson's A-reduced and S-reduced Hamiltonians in the Ir representation with root-mean-square (rms) deviations of 0.000237 and 0.000262 cm−1 respectively. Furthermore, 483 infrared transitions of the 2ν12-ν12 band were fitted using both A-reduced and S-reduced Hamiltonians in the Ir representation with rms deviation of 0.000186 cm−1. From this rovibrational analysis, the rovibrational constants of the v12 = 1 state up to sextic terms were derived for the first time. The band centers of the ν12 band of CH2NOD were found to be 303.319556(15) and 303.319553(18) cm−1 in the A-reduced and S-reduced Hamiltonians respectively, while band centers of 2ν12-ν12 were 296.620976(67) and 296.620976(67) cm−1 respectively. The rovibrational constants of the ground state of CH2NOD in the A-reduced and S-reduced Hamiltonians were obtained for the first time through the fitting of 608 ground state combination differences (GSCDs) derived from the infrared transitions of the ν12 band, together with 11 previously reported microwave frequencies. The rms deviations of the GSCD fit was 0.000318 and 0.000319 cm−1 in the A-reduced and S-reduced Hamiltonians respectively. Additionally, rotational constants and higher order centrifugal distortion terms of the ground, v12 = 1, and v12 = 2 states of CH2NOD were computed from theoretical anharmonic calculations at two different levels of theory, B3LYP and MP2 with the cc-pVTZ basis set, for comparison with the experimental results. The calculated and experimental rovibrational constants of CH2NOD for the ground, v12 = 1, and v12 = 2 states are in close agreement.

High-resolution Fourier transform infrared (FTIR) spectroscopy of formaldoxime-13C (13CH2NOH): Ground and [formula omitted] states rovibrational constants

The high-resolution Fourier transform infrared (FTIR) spectrum of formaldoxime-13C (13CH2NOH) was recorded in the 840–930 cm−1 region with an unapodized resolution of 0.0019 cm−1 for a rovibrational analysis. In the analysis of the dominantly A-type ν8 band, a total of 1025 infrared transitions were fitted using the Watson's A-reduced and S-reduced Hamiltonians in the Ir representation with a root-mean-square (rms) deviations of 0.000430 cm−1 and 0.000431 cm−1 respectively. From the rovibrational analysis, the ν8 = 1 states rotational constants (A, B and C), five quartic terms (ΔJ, ΔJK, ΔK, δJ, δK) and one sextic term (ΦKJ) were derived for the first time. The band center of the ν8 band of 13CH2NOH was found to be 890.235170(25) cm−1 and 890.235182(25) cm−1 in the A-reduced and S-reduced Hamiltonians respectively. Ground state rovibrational constants except for rotational constants B and C were obtained for the first time through the fitting of 443 ground state combination differences (GSCDs) derived from the infrared transitions of the ν8 band of 13CH2NOH, together with 2 previously reported microwave frequencies. The rms deviation of the GSCD fits was the same at 0.000430 cm−1 for both A-reduced and S-reduced Hamiltonians. Furthermore, rovibrational constants up to 5 quartic centrifugal distortion terms of the ground state, and the band center and rotational constants (A, B and C) of the ν8 = 1 state were computed from theoretical anharmonic calculations at two different levels of theory, B3LYP and MP2 with the cc-pVTZ basis set. Good agreement was found between the experimental and calculated rovibrational constants of 13CH2NOH for both ground and ν8 = 1 states.

Ro-vibrational energy analysis of Manning–Rosen and Pöschl–Teller potentials with a new improved approximation in the centrifugal term

Two physically important potentials (Manning-Rosen and P\"oschl-Teller) are considered for the ro-vibrational energy in diatomic molecules. An improved new approximation is invoked for the centrifugal term, which is then used for their solution within the Nikiforov-Uvarov framework. This employs a recently proposed scheme, which combines the two widely used Greene-Aldrich and Pekeris-type approximations. Thus, approximate analytical expressions are derived for eigenvalues and eigenfunctions. The energies are examined with respect to two approximation parameters, $\lambda$ and $\nu$. The original approximations are recovered for certain specials values of these two parameters. This offers a simple effective scheme for these and other relevant potentials in quantum mechanics.

Fourier transform infrared (FTIR) spectroscopy of formaldoxime (CH2NOH) in the 450–3800 cm−1 region and its [formula omitted] band

The Fourier transform infrared (FTIR) spectrum of formaldoxime (CH2NOH) was recorded in the 700–3800 cm−1 region at the Australian Synchrotron with an unapodized resolution of 0.5 cm−1 to identify its fundamental and overtone bands and to measure their relative infrared (IR) intensities in this region. The high-resolution FTIR spectrum of the ν9 band of CH2NOH was also recorded with an unapodized resolution of 0.00096 cm−1 in the 450–600 cm−1 region for a rovibrational analysis. In the analysis of the A/B-hybrid type ν9 band, a total of 2011 infrared transitions (1655b-type and 356 a-type transitions) were fitted using the Watson's A-reduced and S-reduced Hamiltonians in the Ir representation with a root-mean-square (rms) deviation of 0.000096 cm−1 and 0.000305 cm−1 respectively. From this rovibrational analysis, the v9 = 1 state rotational constants (A, B and C) and five quartic terms (ΔJ, ΔJK, ΔK, δJ, δK) were improved from previous work and three sextic terms (ΦJK, ΦKJ, ΦK) were derived for the first time. The band center of the ν9 band of CH2NOH was found to be 530.0187764(63) cm−1 and 530.018762(18) cm−1 in the A-reduced and S-reduced Hamiltonians respectively. All five quartic and three sextic (ΦJK, ΦKJ, ΦK) centrifugal distortion terms of the ground state of CH2NOH were also improved with higher accuracy. They were obtained through the fitting of 3020 ground state combination differences (GSCDs) derived from the IR transitions of the ν9, ν12 and ν10 bands of CH2NOH, together with 23 previously reported microwave frequencies. The rms deviation of this GSCD fit was 0.000498 cm−1 and 0.000519 cm−1 in the A-reduced and S-reduced Hamiltonians respectively. Additionally, rotational constants and higher order centrifugal distortion terms of the ground and v9 = 1 states were computed from theoretical anharmonic calculations at two different levels of theory, B3LYP and MP2 with the cc-pVTZ basis set, for comparison with the experimental results. The calculated and experimental rovibrational constants of CH2NOH for both ground and v9 = 1 states were in good agreement.

Laser cooling and electronic structure studies of CaK and its ions CaK±

Aiming at a laser cooling investigation, we have used ab initio complete active space self consistent field (CASSCF)/(MRCI +Q) calculations to study the electronic structure of the diatomic molecule CaK and its molecular ions CaK+ and CaK−. The potential energy curves and the static dipole moment curves have been investigated for the considered molecules along with the spectroscopic constants T e, ω e, B e, and R e, in addition to the values of dipole moment μ e and dissociation energy D e. Overall, 19 and 14 electronic states have been studied respectively for CaK, CaK+, from which 12 for CaK and six for CaK+ have been investigated here for the first time. Our obtained results agree well with data related to states that have been previously examined. Nineteen electronic states have been explored for CaK−, which up to our knowledge have not been previously calculated. The transition dipole moments have been calculated for the lowest Σ+–Σ+ and Σ+–Π transitions along with the Franck–Condon factor, Einstein coefficient, the spontaneous radiative lifetime, and the emission oscillator strength corresponding to the investigated transitions. A ro-vibrational analysis has been done via the canonical function approach, where the vibrational parameters E v, B v, D v, and the turning points R min and R max have been determined. These calculations showed that the molecule CaK is a suitable candidate for Doppler laser cooling, and we propose a laser cooling scheme to this end. The Doppler limit temperature T D and recoil temperature T r have values as low as T D = 51 μK and T r = 156 nK. The results should provide a useful reference for experimental spectroscopic and ultra-cold molecular physics studies.

Intermolecular dynamics of NH3-rare gas complexes in the ν2 umbrella region of NH3 investigated by rovibrational laser jet-cooled spectroscopy and ab initio calculations.

High resolution jet-cooled spectroscopy experiments have been realized to investigate the intermolecular dynamics of van der Waals (vdW) heterodimers between NH3 and rare gas (Rg) atoms in the ν2 umbrella mode region of NH3. With respect to a previous study dedicated to NH3-Ar [Asselin et al. Mol. Phys. 116, 3642 (2018)], the sensitivity and spectral resolution of our laser spectrometer coupled to a pulsed supersonic jet have been significantly improved to derive more accurate excited state spectroscopic parameters from rovibrational analyses. In addition, we calculated the ground and ν2 excited vibration-rotation-tunneling (VRT) states of these complexes on the four-dimensional ab initio potential energy surfaces from Loreau et al. [J. Chem. Phys. 141, 224303 (2014), ibid. 143, 184303 (2015).] Transition frequencies and intensities of the allowed ν2 = 1 ← 0 transitions obtained from the calculated energy levels and wave functions agree well with the experimental data and are helpful in their analysis. By means of a pseudodiatomic model with the assumption of weak Coriolis coupling, the rovibrational analysis of both the Πe/f(j = 1,k = 0) ←Σf(j = 0,k = 0) and Σf(j = 1,k = 0) ←Σf(j = 0,k = 0) transitions in ortho NH3-Rg (Rg = Ne, Ar, Kr, Xe) complexes enabled us to determine reliable excited state parameters and derive accurate values of the effective vdW bond length Reff, force constant ks, and vdW stretching frequency νs. Comparison between the experimental structural parameters and those from the ab initio calculated VRT levels shows good agreement for NH3-Ne, NH3-Ar and NH3-Kr, and a similar variation of Reff, ks, and νs with the polarizability of Rg in the ground and ν2 excited states. Anomalously small values of νs and ks derived for NH3-Xe in the Πe/f(j = 1,k = 0) state suggest that the applied model is not valid in this case, due to the presence of another state coupling to the perturbed Πf state. Such a state could not be found, however.