Vibration-rotation Interaction Constants Research Articles

The molecular structure and spectroscopic properties of formaldoxime (CH2NOH)

Formaldoxime (CH2NOH) belongs to the possible interstellar molecules. Its isomerization, spectroscopic properties as well as the potential for pumped laser action has long received a lot of attention. Herein, the benchmark database of the spectroscopic constants and anharmonic force fields has been achieved for trans- and cis- formaldoxime. Evaluation is done by using the coupled-cluster theory [CCSD(T)] and density functional theory (B3LYP and B2PLYP), and different basis sets [cc-pVTZ, aug-cc-pVTZ, 6-311+G**, 6-311++G (3df,3pd)] are utilized. The calculated spectroscopic constants commendably reproduce previous experimental results. Besides, a series of vital anharmonic parameters such as vibration-rotation interaction constants, etc, has been provided, which is used for the in-depth study of high-resolution rovibronic spectrum of formaldoxime.

Rotational Spectroscopy of 1-Cyano-2-methylenecyclopropane (C5H5N)─A Newly Synthesized Pyridine Isomer.

The gas-phase rotational spectrum of 1-cyano-2-methylenecyclopropane (C1, C5H5N), an isomer of pyridine, is presented for the first time, covering the range from 235 to 500 GHz. Over 3600 a-, b-, and c-type transitions for the ground vibrational state have been assigned, measured, and least-squares fit to partial-octic A- and S-reduced distorted-rotor Hamiltonians with low statistical uncertainty (σfit = 42 kHz). Transitions for the two lowest-energy fundamental states (ν27 and ν26) and the lowest-energy overtone (2ν27) have been similarly measured, assigned, and least-squares fit to single-state Hamiltonians. Computed vibration-rotation interaction constants (B0-Bv) using the B3LYP and MP2 levels of theory are compared with the corresponding experimental values. Based upon our preliminary analysis, the next few vibrationally excited states form one or more complex polyads of interacting states via Coriolis and anharmonic coupling. The spectroscopic constants and transition frequencies presented here form the foundation for both future laboratory spectroscopy and astronomical searches for 1-cyano-2-methylenecyclopropane.

The 235-360 GHz Rotational Spectrum of 1-Oxaspiro[2.5]octa-4,7-dien-6-one─Analysis of the Ground Vibrational State and Its 10 Lowest-Energy Vibrationally Excited States.

The millimeter-wave rotational spectrum of 1-oxaspiro[2.5]octa-4,7-dien-6-one (1) was collected from 235 to 360 GHz. With the rotational spectrum of this compound available for the first time, more than 5500 a- and c-type transitions were observed and assigned for the vibrational ground state. These transitions were least-squares fit to S- and A-reduced, sextic distorted-rotor Hamiltonians in the Ir representation (σfit = 37 kHz). Additionally, transitions of four fundamental states (ν22, ν21, ν39, and ν38), four overtone states (2ν22, 3ν22, 4ν22, and 5ν22), and two combination states (ν22 + ν21 and ν22 + ν39) were measured, assigned, and least-squares fit to single-state, S- and A-reduced, sextic distorted-rotor Hamiltonians in the Ir representation (σfit < 42 kHz). The computed vibration-rotation interaction constants (B0 - Bv) (MP2 and B3LYP/6-311+G(2d,p)) were compared to their corresponding experimental values, showing excellent agreement for all fundamental states. Based on the intensities of the transitions from six members of the v ν22 series, the fundamental frequency of ν22 was determined to be 79.0 (2.1) cm-1.

Molecular structure and spectroscopic properties of two radicals of C4H2N: a DFT study.

The cyano propargyl radical (CH2C3N and HC3HCN) is important reaction intermediate in both combustion flames and extraterrestrial environments such as cold molecular clouds and circumstellar envelopes of carbon stars. The acquisition of spectroscopic constants and anharmonic effect facilitates a more in-depth study of this radical. However, the data available in the literature do not allow the precise predictions for it in the interstellar medium. In this work, complete spectroscopic parameters as well as anharmonic constants of two radicals of C4H2N have been evaluated by different DFT methods. The calculated results show that it is reasonable to study the molecular spectroscopic properties of C4H2N by wB97XD/6-311++G theoretical level. On this basis, the sextic centrifugal distortion constants, anharmonic constants, vibration-rotation interaction constants, and so on are predicted for the study of high-precision rovibrational spectrum. In addition, the relationship between the anharmonic effect and vibration mode of CH2C3N and HC3HCN and their infrared spectroscopic characteristics are discussed. The calculation of the anharmonic force fields and spectroscopy properties was performed using B3LYP, B3PW91, CAM-B3LYP, and wB97XD methods combined with the 6-311++G and aug-ccpVTZ basis sets, respectively, by the Gaussian16 program suite. The IR spectra were performed with Multiwfn3.8.

Vibrationally excited states of 1H- and 2H-1,2,3-triazole isotopologues analyzed by millimeter-wave and high-resolution infrared spectroscopy with approximate state-specific quartic distortion constants.

In this work, we present the spectral analysis of 1H- and 2H-1,2,3-triazole vibrationally excited states alongside provisional and practical computational predictions of the excited-state quartic centrifugal distortion constants. The low-energy fundamental vibrational states of 1H-1,2,3-triazole and five of its deuteriated isotopologues ([1-2H]-, [4-2H]-, [5-2H]-, [4,5-2H]-, and [1,4,5-2H]-1H-1,2,3-triazole), as well as those of 2H-1,2,3-triazole and five of its deuteriated isotopologues ([2-2H]-, [4-2H]-, [2,4-2H]-, [4,5-2H]-, and [2,4,5-2H]-2H-1,2,3-triazole), are studied using millimeter-wave spectroscopy in the 130-375GHz frequency region. The normal and [2-2H]-isotopologues of 2H-1,2,3-triazole are also analyzed using high-resolution infrared spectroscopy, determining the precise energies of three of their low-energy fundamental states. The resulting spectroscopic constants for each of the vibrationally excited states are reported for the first time. Coupled-cluster vibration-rotation interaction constants are compared with each of their experimentally determined values, often showing agreement within 500kHz. Newly available coupled-cluster predictions of the excited-state quartic centrifugal distortion constants based on fourth-order vibrational perturbation theory are benchmarked using a large number of the 1,2,3-triazole tautomer isotopologues and vibrationally excited states studied.

Energy Landscape and Structural and Spectroscopic Characterization of Diazirine and Its Cyclic Isomers

Identifying new nitrogenated hydrocarbon molecules in the interstellar medium (ISM) is challenging because of the lack of comprehensive spectroscopic data from experiments. In this computational work, we focus on investigating the structures, relative energies, spectroscopic constants, and energy landscape of the cyclic isomers of diazirine (c-CH2N2) using ab initio quantum chemical methods. Density functional theory (DFT) methods and coupled cluster theory with singles and doubles including perturbative triples [CCSD(T)] and CCSD(T) with the explicitly correlated F12b correction [CCSD(T)-F12b] were employed for this purpose along with large correlation consistent cc-pVTZ, cc-pVQZ, and cc-pV5Z basis sets. Harmonic vibrational frequencies, infrared vibrational intensities, rotational constants, and dipole moments are reported. Anharmonic vibrational fundamentals along with centrifugal distortion constants, and vibration-rotation interaction constants are also reported for all the cyclic isomers. The energies computed with the CCSD(T) and CCSD(T)-F12b methods were extrapolated to the one-particle complete basis set (CBS) limit following a three-point formula. At the CCSD(T)-F12b/CBS level of theory, the 3,3H-diazirine (c-CH2N2) is the lowest energy cyclic isomer followed by 1,3H-diazirine, (E)-1,2H-diazirine, and (Z)-1,2H-diazirine, which are 20.1, 47.8, and 51.3 kcal mol-1 above the 3,3H-diazirine, respectively. Accurate structures and spectroscopic constants that are reported here could be useful for future identification of these cyclic nitrogenated organic molecules in the interstellar medium or circumstellar disks.

The molecular structure and spectroscopic properties of C3H2O and its isomers: An ab initio study

The spectroscopic parameters and anharmonic force fields of three isomers (c-H2C3O, HCCCHO and CH2CCO) of C3H2O have been calculated by Density Functional Theory (B3LYP, CAM-B3LYP, wB97XD) and second-order Møller-Plesset perturbation theory (MP2) combining with 6–311++G (3df, 3pd) and aug-cc-pVTZ basis sets. The equilibrium geometries, energies, rotational constants, harmonic and fundamental frequencies, and centrifugal distortion constants of three isomers of C3H2O are calculated and compared with the existed results. The anharmonic constants, vibration–rotation interaction constants, Coriolis coupling constants and force constants of three isomers of C3H2O are firstly predicted. The ingredients of complex vibration modes, and infrared spectral characteristics of three isomers as well as the relationship between structure and spectroscopic properties are detailedly discussed.

Ab initio study of spectroscopic properties at anharmonic force fields of LiNH2.

This work presents a systematic investigation of the spectroscopic properties at anharmonic force fields of ground electronic state ([Formula: see text]) of LiNH2, which are calculated using second-order Møller-Plesset perturbation theory (MP2) and density functional theory (DFT) with hybrid GGA and meta-hybrid GGA (M06-2X) exchange-correlation functional. Two high angular momentum basis sets of 6-311+g (2d, p) and 6-311++g (3df, 2pd) are used. The equilibrium geometries, ground-state rotational constants, harmonic frequencies, and quartic and sextic centrifugal distortion constants of LiNH2 are calculated and compared with corresponding experimental or theoretical data. The predicted accuracy of the calculated constants has been confirmed by analyzing the deviations with respect to experiment. In addition, the anharmonic constants, vibration-rotation interaction constants, force constants, and Coriolis coupling constants of LiNH2 are firstly obtained. The infrared spectrum is predicted and together with the first prediction on the higher-order anharmonic constants contributes to a better understanding of the vibrational and rotational characteristics of LiNH2, thus revealing its internal structure. Graphical abstract The IR spectra and the magnified IR spectra at 3500 cm-1 in harmonic approximations of LiNH2 using B3P86, M06-2X and MP2 methods combining with 6-311++g(3df,2pd).

An analysis of the rotational ground state and lowest-energy vibrationally excited dyad of 3-cyanopyridine: Low symmetry reveals rich complexity of perturbations, couplings, and interstate transitions

The rotational spectrum of 3-cyanopyridine from 130 to 360 GHz was recorded, and an analysis of the ground state and two lowest-energy excited vibrational states was completed. Almost 6700 new transitions were measured for the ground state and fit to a partial octic, distorted-rotor Hamiltonian with low error (σfit < 0.05 MHz). The first two excited vibrational states, ν30 and ν21, are an isolated dyad that exhibits both a- and b-type Coriolis perturbations and requires a two-state, least-squares fit to fully predict the rotational spectrum and determine accurate spectroscopic constants. Quartic and sextic distortion constants were determined for the dyad, along with seven symmetry-allowed perturbation terms: Ga,GaJ,Fbc,FbcK,Gb,GbJ, and GbK. Numerous resonances, including those following a-type selection rules, ΔKa = 2 or ΔKa = 4, and b-type selection rules, ΔKa = 3 or ΔKa = 5, were observed and fit. For ν30 and ν21, the energy difference (ΔE30,21 = 15.7524693 (37) cm−1), both Coriolis coupling constants (ζ30,21a = 0.8327 (9) and ζ30,21b = −0.0181 (3)), and vibration–rotation interaction constants were determined experimentally and compared to theoretical values determined computationally. Combined with the work on the vibrationally excited dyads of 4-cyanopyridine, phenyl isocyanide, benzonitrile, and phenylacetylene, the coupling in ν30 and ν21 provides an opportunity to compare the Coriolis interactions of these analogous mono-substituted aromatic molecules in unusual detail. Additionally, this work improves the ground-state rotational constants and centrifugal distortion constants of 3-cyanopyridine and provides the fundamental constants needed to support an astronomical search for 3-cyanopyridine in the interstellar medium.

Studies on spectroscopic constants for H2PO and D2PO free radicals

This work presents a systematic theoretical study on the calculation of the spectroscopic constants of H2PO and D2PO free radicals, computed with Density Functional Theory (DFT). Different functionals of B3LYP, CAM-B3LYP, CAM-B3LYP-D3(BJ), B3LYP-D3(BJ), and wB97XD are employed and discussed in details. Our results of CAM-B3LYP/ cc-pVQZ are in nice agreement with the experiment. The remarkable isotope effect is addressed and discussed. The nice results demonstrate that our predicted values of anharmonic constants and vibrational frequencies, centrifugal distortion constants, vibration-rotation interaction constants, and unknown anharmonic force field of H2PO and D2PO free radicals are accurate enough to provide a theoretical support.

Molecular structure determination: Equilibrium structure of pyrimidine (m-C4H4N2) from rotational spectroscopy (re SE) and high-level ab initio calculation (re) agree within the uncertainty of experimental measurement.

The pure rotational spectrum of pyrimidine (m-C4H4N2), the meta-substituted dinitrogen analog of benzene, has been studied in the millimeter-wave region from 235 GHz to 360 GHz. The rotational spectrum of the ground vibrational state has been assigned and fit to yield accurate rotational and distortion constants. Over 1700 distinct transitions were identified for the normal isotopologue in its ground vibrational state and least-squares fit to a partial sextic S-reduced Hamiltonian. Transitions for all four singly substituted 13C and 15N isotopologues were observed at natural abundance and were likewise fit. Deuterium-enriched samples of pyrimidine were synthesized, giving access to all eleven possible deuterium-substituted isotopologues, ten of which were previously unreported. Experimental values of rotational constants and computed values of vibration-rotation interaction constants and electron-mass corrections were used to determine semi-experimental equilibrium structures (re SE) of pyrimidine. The re SE structure obtained using coupled-cluster with single, double, and perturbative triple excitations [CCSD(T)] corrections shows exceptional agreement with the re structure computed at the CCSD(T)/cc-pCV5Z level (≤0.0002 Å in bond distance and ≤0.03° in bond angle). Of the various computational methods examined, CCSD(T)/cc-pCV5Z is the only method for which the computed value of each geometric parameter lies within the statistical experimental uncertainty (2σ) of the corresponding semi-experimental coordinate. The exceptionally high accuracy and precision of the structure determination is a consequence of the large number of isotopologues measured, the precision and extent of the experimental frequency measurements, and the sophisticated theoretical treatment of the effects of vibration-rotation coupling and electron mass. Taken together, these demanding experimental and computational studies establish the capabilities of modern structural analysis for a prototypical monocyclic aromatic compound.

Determination of a semi-experimental equilibrium structure of 1-phosphapropyne from millimeter-wave spectroscopy of [formula omitted] and [formula omitted

Trideuterated 1-phosphapropyne (CD3CP) has been produced by co-pyrolysis of phosphorus trichloride and esadeuterated ethane. The rotational spectra of CD3CP in the ground and the low-lying vibrational states v8 (CCP bending mode) and 2 v8 have been investigated in the millimeter-wave region. Very accurate values of the quartic centrifugal distortion constants DJ and DJK and of the sextic distortion constants HJK and HKJ have been obtained for the ground state. l-type resonance effects have been taken into account in the analysis of the spectra of the degenerate bending states, so that the energy difference between the v8|l| = 20, and v8|l| = 22 states could be determined, together with a number of spectroscopic constants involved in the l-type resonance. Moreover, for the parent isotopologue CH3CP a new set of excited-state lines (v8 = 1, 2 and v4 = 1) were recorded up to 330 GHz, and a global analysis including all available rotational and rovibrational transitions related to the ground and v8 = 1, 2 states has been performed. A satisfactory fit could only be obtained by making a reassignment of the few transition wavenumbers previously measured for the 2ν80←ν8±1 hot band [M.K. Bane et al., J. Mol. Spectrosc.275 (2012) 9–14].The experimental work has been combined with quantum-chemical computations. Quadratic and cubic force constants of 1-phosphapropyne have been calculated at MP2 level of theory with a basis set of triple-ζ quality. A semi-experimental equilibrium structure has been derived by correcting experimental ground-state rotational constants by means of theoretical vibration-rotation interaction constants.

Spectroscopic constants and anharmonic force fields of F2SO: An ab inito study

The equilibrium geometry, spectroscopic constants and anharmonic force field of F2SO (X∼1A′) have been reported employing B3LYP, B3P86, B3PW91 and MP2 methods combining with Dunning’s correlation-consistent cc-pVQZ, cc-pV5Z, aug-cc-pVQZ and aug-cc-pV5Z basis sets. The calculated equilibrium geometry, equilibrium rotational constants and fundamental vibrational frequencies of F2SO well reproduce the previous theoretical or experimental values. The calculated equilibrium geometry verifies that F2SO has pyramidal structure and Cs symmetry instead of C1 symmetry. The ground-state rotational constants, harmonic vibrational frequencies, anharmonic constants, quartic and sextic centrifugal distortion constants, cubic and quartic force constants, vibration-rotation interaction constants, and Coriolis coupling constants of F2SO are also predicted. The calculated results show that B3P86 and MP2 methods are superior to B3LYP and B3PW91 methods for the spectroscopic constants of F2SO, we hope that our predictions can provide the useful data for the experiment study of the corresponding spectroscopic constants of F2SO.

Millimeter-wave spectroscopy of the chlorine isotopologues of 2-chloropyridine and twenty-three of their vibrationally excited states

A combined total of 25 vibrational states of 2-chloropyridine (C5H4NCl, μa = 3.07 D, μb = 1.70 D), including states for both chlorine isotopologues, have been least-squares fit to sextic, A-reduced Hamiltonians with low error (<0.05 MHz). In total, over 22,500 transition frequencies were measured in the 135–375 GHz frequency region. The technique of fixing undeterminable distortion constants to the corresponding values of the ground vibrational state for fundamental states and to extrapolated values for overtone and combination states was employed. The experimentally determined rotational, centrifugal distortion, and vibration-rotation interaction constants are reasonably well-predicted by computational methods (B3LYP/6-311+G(2d,p)). For the chlorine isotopologues, the changes in rotational and quartic distortion constants upon vibrational excitation are quite similar, indicating that it is possible to estimate the constants of a lower-abundance isotopologue’s excited vibrational state using the change in constant observed in the higher-abundance isotopologue. The changes in rotational and quartic distortion constants upon vibrational excitation are also quite similar between analogous vibrational states of 2-chloropyridine and chloropyrazine, despite their differences in molecular composition.

Riddles of the structure and vibrational dynamics of HO3 resolved near the ab initio limit.

The hydridotrioxygen (HO3) radical has been investigated in many previous theoretical and experimental studies over several decades, originally because of its possible relevance to the tropospheric HOx cycle but more recently because of its fascinating chemical bonding, geometric structure, and vibrational dynamics. We have executed new, comprehensive research on this vexing molecule via focal point analyses (FPA) to approach the ab initio limit of optimized geometric structures, relative energies, complete quartic force fields, and the entire reaction path for cis-trans isomerization. High-order coupled cluster theory was applied through the CCSDT(Q) and even CCSDTQ(P) levels, and CBS extrapolations were performed using cc-pVXZ (X = 2-6) basis sets. The cis isomer proves to be higher than trans by 0.52 kcal mol-1, but this energetic ordering is achieved only after the CCSDT(Q) milestone is reached; the barrier for cis → trans isomerization is a minute 0.27 kcal mol-1. The FPA central re(O-O) bond length of trans-HO3 is astonishingly long (1.670 Å), consistent with the semiexperimental re distance we extracted from microwave rotational constants of 10 isotopologues using FPA vibration-rotation interaction constants (αi). The D0(HO-O2) dissociation energy converges to a mere 2.80 ± 0.25 kcal mol-1. Contrary to expectation for such a weakly bound system, vibrational perturbation theory performs remarkably well with the FPA anharmonic force fields, even for the torsional fundamental near 130 cm-1. Exact numerical procedures are applied to the potential energy function for the torsional reaction path to obtain energy levels, tunneling rates, and radiative lifetimes. The cis → trans isomerization occurs via tunneling with an inherent half-life of 1.4 × 10-11 s and 8.6 × 10-10 s for HO3 and DO3, respectively, thus resolving the mystery of why the cis species has not been observed in previous experiments executed in dissipative environments that allow collisional cooling of the trans-HO3 product. In contrast, the pure ground eigenstate of the cis species in a vacuum is predicted to have a spontaneous radiative lifetime of about 1 h and 5 days for HO3 and DO3, respectively.

Millimeter-wave spectroscopy of the chlorine isotopologues of chloropyrazine and twenty-two of their vibrationally excited states

The measurement of over 24,000 new rotational transitions of chloropyrazine (C4H3N2Cl, μa = 1.55 D, μb = 0.14 D) in the 130–375 GHz frequency region enabled the assignments of the rotational spectra for the ground vibrational states of the [35Cl]- and [37Cl]-isotopologues and a combined total of 22 low-energy excited vibrational states. These vibrational states have been fit to sextic A-reduced Hamiltonians with low error (<0.05 MHz). These data allow for precise determination of the vibration-rotation interaction constants for the six lowest-energy fundamental vibrational modes (ν24, ν17, ν23, ν16, ν22, and ν15) of the [35Cl]-isotopologue and the four lowest-energy fundamental vibrational modes (ν24, ν17, ν23, and ν16) of the [37Cl]-isotopologue. In addition, many combination and overtone states were observed, bringing the total number of excited states to seventeen for the [35Cl]-isotopologue and five for the [37Cl]-isotopologue. The spectroscopic constants for the ground state, ν24, and ν17 for each isotopologue are very well determined (Nlines > 1400 for each least-squares fit). The vibration-rotation interaction constants experimentally determined for all observed fundamentals are generally in quite close agreement with their predicted (B3LYP/6-311+G(2d,p)) values.

Theoretical study of anharmonic force field and spectroscopic constants for 1-chlorophosphaethene, CH2PCl and CD2PCl

The anharmonic force field and spectroscopy constants for CH2PCl are determined using CCSD(T), VPT2, and density functional theory employing cc-pVQZ basis sets. The molecule structure, rotational spectroscopic constants, and vibrational wave numbers are compared with the available experimental data. Anharmonicity constants, vibration-rotation interaction constants and cubic force constants are predicted. Vibrational wave numbers and rotational constants for CD2PCl are also determined using the same levels. The isotopic shifts of vibrational wave numbers are remarkable by D atom substitution for 1-chlorophosphaethene.

Ab Initio Studies on Spectroscopic Constants for the HAsO Molecule.

The anharmonic force fields and spectroscopic constants of the electronic ground state (X̃1A') for the HAsO molecule are reported employing the MP2, B3LYP, B3P86, and B3PW91 methods with cc-pVQZ and cc-pV5Z basis sets. The calculated molecular geometries, rotational constants, vibrational frequencies, and anharmonic constants of the HAsO molecule are compared with the experimental data. It is found that the best agreement between the calculated results and experiment data is at the B3LYP/cc-pV5Z theoretical level. The predicted cubic and quartic force fields, vibration-rotation interaction constants, quartic and sextic centrifugal distortion constants, and Coriolis coupling constants of the HAsO molecule at the B3LYP/cc-pV5Z theoretical level are expected to be reliable.

The high-resolution infrared spectrum of the [formula omitted] combination band of jet-cooled propyne

We present the first detection of the high-resolution ro-vibrational spectrum of the ν3+ν5 combination band of propyne around 3070cm−1. The fully resolved spectrum is recorded for supersonically jet-cooled propyne using continuous wave cavity ring-down spectroscopy (cw-CRDS). The assignments are supported with the help of accurate ab initio vibration-rotation interaction constants (αi) and anharmonic frequencies. A detailed analysis of the rotationally cold spectrum is given.

Computational anharmonic force fields of CuSH and CuSD

The anharmonic force fields and spectroscopy constants for the ground electronic state of copper hydrosulfide (CuSH) have been investigated using various theoretical methods (MP2, B3LYP, B3P86, B3PW91) and basis sets (cc-pVDZ, cc-pVTZ). It turns out that the MP2/cc-pVTZ theoretical level is reasonable to study the molecular spectroscopic properties of CuSH. The calculated molecular structure, rotational constants, vibrational frequencies, centrifugal distortion constants, vibration–rotation interaction constants, force constants and Coriolis coupling constants of CuSH can be utilized to provide theoretical predictions of the spectroscopic properties and can be conducive to chemical applications such as the hydrodesulfurisation of fossil feed-stocks. Besides, the calculated force constants, evaluated in mass-weighted normal coordinates using a finite-difference approach, can be used to analyze the potential energy surface of CuSH. In addition, the anharmonic force fields of CuSD have been also investigated using the MP2 method.