Rovibrational Structure Research Articles

Determination of the Interaction Potential and Rovibrational Structure of the Ground Electronic State of MgAr+ Using PFI-ZEKE Photoelectron Spectroscopy

The interaction potential characterizing the ground electronic state of MgAr+ has been determined from the photoelectron spectrum recorded from the a 3Π0 metastable state of MgAr at high resolution by pulsed-field-ionization zero-kinetic-energy (PFI-ZEKE) photoelectron spectroscopy. The photoelectron spectrum provides information on the first ten vibrational levels of MgAr+ and leads to the determination of the adiabatic ionization energy of metastable MgAr (38 742.3(20) cm-1), the ground state dissociation energy of MgAr+ (1254(60) cm-1), and to the characterization of the rovibrational photoionization dynamics of MgAr.

High-Resolution Infrared Synchrotron Investigation of (HCN)2 and a Semi-Experimental Determination of the Dissociation Energy D0.

The high‐resolution infrared absorption spectrum of the donor bending fundamental band ν 61 of the homodimer (HCN)2 has been collected by long‐path static gas‐phase Fourier transform spectroscopy at 207 K employing the highly brilliant 2.75 GeV electron storage ring source at Synchrotron SOLEIL. The rovibrational structure of the ν 61 transition has the typical appearance of a perpendicular type band associated with a Σ–Π transition for a linear polyatomic molecule. The total number of 100 assigned transitions are fitted employing a standard semi‐rigid linear molecule Hamiltonian, providing the band origin ν 0 of 779.05182(50) cm−1 together with spectroscopic parameters for the degenerate excited state. This band origin, blue‐shifted by 67.15 cm−1 relative to the HCN monomer, provides the final significant contribution to the change of intra‐molecular vibrational zero‐point energy upon HCN dimerization. The combination with the vibrational zero‐point energy contribution determined recently for the class of large‐amplitude inter‐molecular fundamental transitions then enables a complete determination of the total change of vibrational zero‐point energy of 3.35±0.30 kJ mol−1. The new spectroscopic findings together with previously reported benchmark CCSDT(Q)/CBS electronic energies [Hoobler et al. ChemPhysChem. 19, 3257–3265 (2018)] provide the best semi‐experimental estimate of 16.48±0.30 kJ mol−1 for the dissociation energy D 0 of this prototypical homodimer.

High resolution analysis of GeH4 in the dyad region: Ro-vibration energy structure of 70GeH4 and line strengths of MGeH4 (M = 70, 72, 73, 74, 76)

The infrared spectrum of MGeH4 (M=70,72,73,74,76) was measured at the temperature of (294.5 ± 0.3) K in the 740-960 cm−1 region with a Bruker Fourier transform infrared spectrometer IFS125 and analyzed. The line positions of the ν2/ν4 bands and the ro-vibrational energy structure of corresponding upper vibrational states of 70GeH4 were analyzed. The strengths of 1079 experimentally recorded spectral lines (243/270/152/262/152 lines for the isotopologues 70GeH4/72GeH4/73GeH4/ 74GeH4/76GeH4) with the value of quantum number Jmax = 19 were determined from the fit of their line shapes with a Hartmann–Tran line profile and were used then in the weighted fit for determination of the effective dipole moment parameters of the ν4 band. The obtained sets of parameters reproduce the initial experimental line intensities with the drms=3.46/3.12/3.21/3.38/3.45/% for the 70GeH4/72GeH4/73GeH4/ 74GeH4/76GeH4 species, respectively. A list of transitions with their line intensities is generated in the HITRAN format up to the value of quantum number J=40.

Quantum-mechanical study of energies, structures and vibrational spectra of the HF complexed with dimethyl ether

Interaction energies, geometry and vibrational frequencies of the gas-phase HF-dimethyl ether complex were obtained using quantum-chemical methods. Equilibrium and vibrationally averaged geometries, harmonic and anharmonic wavenumbers of the complex were calculated using second-order perturbation theory procedures with B3LYP, B2PLYP-D and MP2 methods with 6-311++G(2df, 2pd) basis set. Quantum-mechanical model describing anharmonic-type vibrational couplings within hydrogen bond was used to explain broadening, fine structure and temperature dependence of the FH stretching IR absorption bands as effect of hydrogen bond formation. Simulations of the rovibrational structure of the FH stretching bands were performed for different temperatures. The results were compared with experimental spectra.

AtmoCube A1: airglow measurements in the mesosphere and lower thermosphere by spatial heterodyne interferometry

The Institute for Atmospheric and Environmental Research at the University of Wuppertal and the Institute of Energy and Climate Research Stratosphere at Research Center Juelich developed a CubeSat payload for atmospheric research. The payload consists of a small interferometer for the observation of airglow near 762 nm. The line intensities of the oxygen A-band are used to derive temperatures in the mesosphere and lower thermosphere region. The temperature data will be used to analyze dynamical wave structures in the atmosphere. The interferometer technology chosen to measure the ro-vibrational structure of the O2 atmospheric band near 762 nm is a spatial heterodyne interferometer originally proposed by Connes in 1958. It can be designed to deliver extraordinary spectral resolution to resolve individual emission lines. The utilization of a two-dimensional imaging detector allows for recording interferograms at adjacent locations simultaneously. Integrated in a six-unit CubeSat, the instrument is designed for limb sounding of the atmosphere. The agility of a CubeSat will be used to sweep the line-of-sight through specific regions of interest to derive a three-dimensional image of an atmospheric volume using tomographic reconstruction techniques.

High Temperature Optical Spectra of Diatomic Molecules at Local Thermodynamic Equilibrium

In the paper, several theoretical approaches to the determination of the reduced absorption and emission coefficients under local thermodynamic equilibrium conditions were exposed and discussed. The full quantum-mechanical procedure based on the Fourier grid Hamiltonian method was numerically robust but time consuming. In that method, all transitions between the bound, free, and quasi-bound states were treated as bound–bound transitions. The semi-classical method assumed continuous energies of ro-vibrational states, so it did not give the ro-vibrational structure of the molecular bands. That approach neglected the effects of turning points but agreed with the averaged-out quantum-mechanical spectra and it was computer time efficient. In the semi-quantum approximation, summing over the rotational quantum number J was done analytically using the classical Franck–Condon principle and the stationary–phase approximation and its consumption of computer time was lower by a few orders of magnitude than the case of the full quantum-mechanical approach. The approximation described well the vibrational but not the rotational structure of the molecular bands. All the above methods were compared and discussed in the case of a visible and near infrared spectrum of LiHe, Li2, and Cs2 molecules in the high temperature range.

Broadband cantilever-enhanced photoacoustic spectroscopy in the mid-IR using a supercontinuum.

We demonstrate cantilever-enhanced photoacoustic spectroscopy in the mid-infrared using a supercontinuum source. The approach is broadband and allows for higher photoacoustic signal intensity and an enhanced signal-to-noise ratio as compared to systems employing conventional black body radiation sources. Using this technique, we perform spectroscopic measurements of the full ro-vibrational band structure of water vapor at 1900nm and methane at 3300nm with relative signal enhancement factors of 70 and 19, respectively, when compared to measurements that use the black body radiation source. Our results offer a novel perspective for photoacoustic detection opening the door to sensitive broadband analyzers in the mid-infrared spectral region.

Rovibrational fine structure and transition dipole moment of CF3H by frequency-comb-assisted saturated spectroscopy at 8.6 µm

We report on rovibrational fine structure spectroscopy of room-temperature trifluoromethane with a saturated absorption method, using a quantum cascade laser at around 8.6 µm phase-locked to a self-referenced mid-infrared frequency comb synthesizer. The absolute line-center frequencies of 36 lines have been measured by means of the wavelength modulation method with a best fractional uncertainty of ∼3×10−9 in a single acquisition scan from 34.7426 to 34.7443 THz. In addition, an extensive investigation of the measured Lamb-dip profiles using both direct pump-probe spectroscopy method and wavelength modulation technique has been performed for two selected lines, rR40(64) and rR36(38), belonging to the υ5 vibrational band, as a function of either the gas pressure or the pump beam power. This approach allowed the measurement of the main spectroscopic parameters, such as saturation intensity, transition electric dipole moment, as well as self-pressure broadening coefficient.

High-resolution infrared spectroscopy of O2H+ in a cryogenic ion trap.

The protonated oxygen molecule, O2H+, and its helium complex, He-O2H+, have been investigated by vibrational action spectroscopy in a cryogenic 22-pole ion trap. For the He-O2H+ complex, the frequencies of three vibrational bands have been determined by predissociation spectroscopy. The elusive O2H+ has been characterized for the first time by high-resolution rovibrational spectroscopy via its ν1 OH-stretching band. Thirty-eight rovibrational fine structure transitions with partly resolved hyperfine satellites were measured (56 resolved lines in total). Spectroscopic parameters were determined by fitting the observed lines with an effective Hamiltonian for an asymmetric rotor in a triplet electronic ground state, X̃3A'', yielding a band origin at 3016.73 cm-1. Based on these spectroscopic parameters, the rotational spectrum is predicted, but not yet detected.

Study of the Rotational Structure of the v2 Inversion Band of the 15NH2D Molecule

The Fourier spectrum of the 15NH2D molecule in the range from 650 to 1150 cm–1, where the ν2 vibrationinversion band is located, is first studied. Analysis of the given band allows the energy rovibrational structure of the examined state to be determined. The inverse spectroscopic problem is solved based on the data obtained.

FTIR spectrum of vinyl fluoride near 3.6 μm: rovibrational analysis of the ν4+ν7 band and modelling Coriolis resonances in a seven-level polyad

ABSTRACTThe Fourier transform infrared (FTIR) spectrum of vinyl fluoride, H2C=CHF, has been widely investigated in the region of the ν4+ν7 combination band around 2800 cm−1 at a resolution of 0.005 cm−1. This vibration of A' symmetry gives rise to an a/b-hybrid band with a predominant a-type component. The rovibrational structure is strongly perturbed and the analysis has been rather complicated since this combination band is involved at least in a seven-level interacting polyad, including the ν8+2ν10, 2ν8+ν10, 2ν7+ν9, ν7+ν8+ν12, ν5+ν9+ν10 and ν7+ν10+ν12 vibrational states. The study has been further complicated by the absence of transitions coming from the perturbers that were considered as dark states. The spectral analysis resulted in the identification of 936 transitions with J" ≤ 46 and Ka" ≤ 11, all belonging to the a-type component. Most of the assigned data have been fitted using the Watson's A-reduction Hamiltonian in the Ir representation and proper Coriolis perturbation operators. The model employed includes seven different resonances within a complex polyad resonant system and a set of spectroscopic constants for the ν4+ν7 combination band, for the dark states, and Coriolis coupling coefficients have been determined.

Theoretical Study of the Feasibility of Laser Cooling the 24Mg35Cl Molecule Including Hyperfine Structure and Branching Ratios.

The possibility of laser cooling the 24Mg35Cl molecule is investigated using the electronic, rovibrational, and hyperfine structure. Twelve low-lying Λ-S electronic states of the 24Mg35Cl molecule have been calculated at the multireference configuration interaction level of theory. The spin-orbit coupling effects are taken into account in the electronic structure calculations. Spectroscopic constants agree well with previously obtained theoretical and experimental values. On the basis of the potential energy curves and transition dipole moments, the highly diagonally distributed Franck-Condon factors for the A2Π → X2Σ+ transition and short radiative lifetime of the A2Π state are determined. Then, employing a quantum effective Hamiltonian approach, we investigate the hyperfine manifolds of the X2Σ+ state and obtain the zero-field hyperfine spectrum with the errors relative to the experimental data not exceeding 8-20 kHz. Finally, we design a laser cooling scheme with one cooling main laser beam and two repumping laser beams with modulated sidebands, which is sufficient for the implementation of efficient laser slowing and cooling of the 24Mg35Cl molecule. Moreover, it is important to note that the dissociation energy (2.2593 eV) of the B2Σ+ state is obtained for the first time at the multireference configuration interaction level. We hope that this can provide a helpful reference for experimental observation.

Exploration of the molecular ro-vibrational energy structure: on the perspective of Yb2 and Cd2 internal cooling, and 171Yb-version of Einstein–Podolsky–Rosen experiment

ABSTRACTSchemes for internal ro-vibrational cooling in Yb2 and Cd2, as well as 171Yb Bohm's spin-1/2 particle version of the Einstein‒Podolsky‒Rosen experiment based on photo-dissociation of (171Yb)2 are presented. The schemes are based on exploration of the rotational and vibrational energy structures using both theoretical and experimental approaches.

Fourier transform infrared spectroscopy of D212CO in the 2500–4500 cm−1 region and the first rovibrational analysis of its v2 = 2 state

A low-resolution (0.5 cm−1) Fourier transform infrared (FTIR) spectrum of formaldehyde-d2 (D212CO) in the 2500–4500 cm−1 region was recorded to study the combination bands in this region. The bands ν2+ν4,ν2+ν6, ν2+ν3, ν1+ν2, ν2+ν5, 3ν3, 2ν2 and 2ν5 were identified and their band centers (with an uncertainty of ± 0.1 cm−1) and band types were determined. Furthermore, the high-resolution FTIR spectrum of the 2ν2 overtone band (3315–3440 cm−1) of D212CO was recorded at an unapodized resolution of 0.0063 cm−1 and its infrared lines were analyzed. A total of 970 rovibrational transitions have been assigned and fitted up to J′ = 35 and Ka′ = 14 using the Watson’s A-reduced Hamiltonian in the Ir representation. Upper state (v2 = 2) rovibrational constants inclusive of three rotational and five quartic centrifugal distortion constants were accurately determined for the first time. The band center of the 2ν2 band was determined as 3385.200666 ± 0.000035 cm−1. The rms deviation of the rovibrational fit was 0.00093 cm−1. From the fitting of 451 ground state combination differences (GSCDs) of D212CO which were derived from the infrared transitions of the 2ν2 band of this work, together with 360 microwave frequencies from a previous study, new and accurate ground state constants of D212CO up to three octic terms were obtained. The combination and overtone bands and the newly assigned high-resolution infrared lines of the 2ν2 band in the 2500–4500 cm−1 region can be used to detect D212CO in this infrared region. In addition, the results derived from this study give information on the rovibrational molecular structure of D212CO.

Investigation of the ro-vibrational energy structure of (0101, F1) and (0101, F2) states of the 28SiH4 molecule

An analysis of the high-resolution vibrational-rotational IR spectrum of ν2 + ν4 (F1) and ν2 + ν4 (F2) bending absorption bands of the 28SiH4 molecule is carried out for the first time using the SPHETOM software. Approximately 618 experimental transitions with Jmax = 8 are assigned to ν2 + ν4 (F1) and ν2 + ν4 (F2) bands. Rotational, centrifugal distortion, tetrahedral splitting, and resonance interaction parameters for these vibrational bands are derived from the weighted fit of experimental line positions. The set of parameters obtained reproduces the initial experimental data with an accuracy close to the experimental uncertainties drms = 8 × 10–4 cm–1.

Spontaneous dissociation and rovibrational structure of the metastable D2− anion

Long-lived rovibrational states of the metastable ${{\mathrm{D}}_{2}}^{\ensuremath{-}}$ molecular anion, with lifetimes of the order of microseconds, were studied by recording the time-of-flight difference between D and ${\mathrm{D}}^{\ensuremath{-}}$ fragments produced by spontaneous dissociation of the ${{\mathrm{D}}_{2}}^{\ensuremath{-}}$ complex. The simulated time-of-flight spectrum was adjusted to the experimental results, allowing us to extract the resonance energy relative to the dissociation threshold. A single value was found, $22.8\ifmmode\pm\else\textpm\fi{}0.3$ meV, which is somewhat larger than resonance energies predicted by theory for long-lived ${{\mathrm{D}}_{2}}^{\ensuremath{-}}$ rovibrational states with $(J,v)$ quantum numbers (37,0), (37,1), and (38,0) [Phys. Rev. A 75, 012507 (2007)]. This discrepancy seems due to the extreme sensitivity of these metastable states to minute features of the potential energy curve. The spectral feature is explained by the competition between autodetachment and spontaneous dissociation decay channels.

Molecular plasmonics: The role of rovibrational molecular states in exciton-plasmon materials under strong-coupling conditions

We extend the model of exciton-plasmon materials to include a ro-vibrational structure of molecules using wave-packet propagations on electronic potential energy surfaces. The new model replaces conventional two-level emitters with more complex molecules allowing to examine the influence of alignment and vibrational dynamics on strong coupling with surface plasmon-polaritons. We apply the model to a hybrid system comprising a thin layer of molecules placed on top of a periodic array of slits. Rigorous simulations are performed for two types of molecular systems described by vibrational bound-bound and bound-continuum electronic transitions. Calculations reveal new features in transmission, reflection and absorption spectra including the observation of significantly higher values of the Rabi splitting and vibrational patterns clearly seen in the corresponding spectra. We also examine the influence of anisotropic initial conditions on optical properties of hybrid materials demonstrating that the optical response of the system is significantly affected by an initial pre-alignment of the molecules. Our work demonstrates that pre-aligned molecules could serve as an efficient probe for the sub-diffraction characterization of the near-field near metal interfaces.

Investigation of the ro-vibrational energy structure of (0101, F1) and (0101, F2) states of 28SiH4 molecule

Investigation of the ro-vibrational energy structure of (0101, F1) and (0101, F2) states of 28SiH4 molecule

Characterising molecules for fundamental physics: an accurate spectroscopic model of methyltrioxorhenium derived from new infrared and millimetre-wave measurements.

Precise spectroscopic analysis of polyatomic molecules enables many striking advances in physical chemistry and fundamental physics. We use several new high-resolution spectroscopic devices to improve our understanding of the rotational and rovibrational structure of methyltrioxorhenium (MTO), the achiral parent of a family of large oxorhenium compounds that are ideal candidate species for a planned measurement of parity violation in chiral molecules. Using millimetre-wave and infrared spectroscopy in a pulsed supersonic jet, a cryogenic buffer gas cell, and room temperature absorption cells, we probe the ground state and the Re[double bond, length as m-dash]O antisymmetric and symmetric stretching excited states of both CH3187ReO3 and CH3185ReO3 isotopologues in the gas phase with unprecedented precision. By extending the rotational spectra to the 150-300 GHz range, we characterize the ground state rotational and hyperfine structure up to J = 43 and K = 41, resulting in refinements to the rotational, quartic and hyperfine parameters, and the determination of sextic parameters and a centrifugal distortion correction to the quadrupolar hyperfine constant. We obtain rovibrational data for temperatures between 6 and 300 K in the 970-1015 cm-1 range, at resolutions down to 8 MHz and accuracies of 30 MHz. We use these data to determine more precise excited-state rotational, Coriolis and quartic parameters, as well as the ground-state centrifugal distortion parameter DK of the 187Re isotopologue. We also account for hyperfine structure in the rovibrational transitions and hence determine the upper state rhenium atom quadrupole coupling constant eQq'.

First study of the ro-vibrational structure of the g-symmetry vibrational states of [formula omitted] from the analysis of hot bands: The [formula omitted] and [formula omitted] bands

The two strongest absorption “hot” bands of C2D4, ν7+ν10−ν10 and ν10+ν12−ν10 were analyzed for the first time on the basis of high resolution infrared spectra recorded with a Bruker high resolution Fourier transform spectrometer. About 740 and 550 transitions (233 and 174 upper state ro-vibrational energy values) with Jmax.=25, Kamax=18 and Jmax.=20, Kamax.=10 for the bands ν7+ν10−ν10 and ν10+ν12−ν10 were assigned. The obtained upper ro-vibrational energies were used then in the weighted fit of parameters of the effective Hamiltonian which takes into account resonance interactions between the vibrational states (v7=v10=1) and (v10=v12=1), on the one hand, and eight other closely located vibrational states, on the other hand. A set of 46 varied parameters was obtained from the fit, which reproduces the initial experimental data with the rms deviation of 2.5×10−4cm−1 and which is close to experimental uncertainties.