Vibration-rotation Spectra Research Articles

The isotope effect of the O 2a1Δg rotational constant

The pure rotational spectrum of a 1 Δ g oxygen in its first excited vibrational state as well as the ground vibrational state rotational spectra of 16O 18O and 18O 2 in their a states have been observed. Precise parameters describing the spectra have been determined and an accurate value has been derived for the equilibrium interatomic distance in the Born-Oppenheimer limit.

Algebraic solution of the vibron model for diatomic molecules

Angular momentum projected mean field theory is used to derive analytic expressions for various matrix elements in the vibron model for diatomic molecules. The results are applied in a search for a realistic description of rotation-vibration spectra in the vibron model.

Infrared diode laser spectroscopy of FDF −

The gas-phase vibration-rotation spectrum of FDF − was observed in the 930 and 1460 cm −1 regions with a tunable diode laser spectrometer. The observed bands in the 930 cm −1 region were assigned to the v 3 antisymmetric stretching and the v 2 bending modes. The 1460 cm −1 region was assigned to the v 1 + v 3 combination band. The previous assignment of the 1397 cm −1 band was corrected to the 2 v 1 + v 3 − v 1 band. All observed transitions were analyzed simultaneously by including a Coriolis interaction between the v 2 and v 3 states to determine molecular constants in the ground as well as v 2, v 3, v 1 + v 3, 2 v 1 + v 3, and v 1 states. The fundamental frequencies were determined to be v 2 = 928.7303(17) cm −1 and v 3 = 934.1933(7) cm −1, with three standard deviations in parentheses. From the rotational constants obtained, the equilibrium F ··· F internuclear distance was calculated to be 2.277 52(10) Å, which agreed with the value (2.277 71(9) Å) of FHF − reported previously.

Infrared diode laser spectroscopy of a high-temperature molecule GeS using spectrum processing by fourier transformation

The vibrational-rotational spectrum of GeS has been observed using a diode laser spectrometer equipped with a heatpipe high-temperature cell of a White cell type. Fringes due to optical reflections inside the high-temperature White cell were inherent in the observation of the spectra. However, they were eliminated, as were high-frequency noises, by Fourier manipulation of the observed diode laser spectrum. About 620 spectral lines for the Δv = 1 band sequences of the eight isotopomers, 74Ge 32S, 72Ge 32S, 70Ge 32S, 73Ge 32S, 76Ge 32S, 74Ge 34S, 72Ge 34S and 70Ge 34S have been assigned between 522 and 593 cm −1. These infrared data combined with 91 microwave data from the literature have been analyzed with a least-squares fit to a Dunham potential function with only 11 parameters which included three Watson type Δ correction terms. The Dunham Y ij coefficients have been derived for each of the eight isotopomers. The equilibrium vibrational frequency ω e of 74Ge 32S is 574.269 313(271) cm −1.

High-Resolution Infrared Spectroscopy of Methyl Isocyanide: The ν3, ν6, and ν7 + ν8 Bands

The vibration-rotation spectrum of methyl isocyanide (CH3NC) has been recorded with the aid of a high-resolution Fourier transform spectrometer in the region 1370 to 1560 cm−1 containing the perpendicular band of the fundamental vibration ν6 (species E), the weaker parallel band of the ν3 (A1) fundamental, and the perpendicular combination band ν∓7 + ν∓8 (E) enhanced by Fermi resonance with ν6. Sixteen hundred seventy well-resolved lines were assigned to 15 subbands of ν6, 6 subbands of ν3, and 3 subbands of ν−7 + ν−8. A strong x, y-Coriolis resonance between ν3 and ν6 and Fermi resonance between ν±6 and the E component ν∓7 + ν∓8, as well as between ν3 and the A1,2 components ν±7 + ν∓8, greatly affects the spectrum. Additional weaker anharmonic interaction of ν6 with the ν4 + 2ν28 combination and higher-order rotational interactions connecting the various states were also detected in the spectrum. All of these interactions have been incorporated into a 9 × 9 Hamiltonian matrix used for modeling the upper states of the observed transitions. A set of spectroscopic constants is reported for the upper states of the bands ν3, ν6, and ν7 + ν8 and for ν4 + 2ν28 which reproduces the observed lines with an overall standard deviation of 0.0012 cm−1.

New Investigations of the A2Δ-X2Π Band System in the CH Radical and a New Reduction of the Vibration-Rotation Spectrum of CH from the ATMOS Spectra

Seven bands of the A2Δ-X2Π system of the CH radical have been photographed in emission from a Geissler tube using conventional spectroscopic techniques. Under high resolution and using Th lines as standards, as well as an interferometric comparator equipped with a photoelectric scanning device, the 0-0, 1-1, 2-2, 0-1, and 1-2 bands have been rephotographed and the 3-3 and 2-3 bands, with a total number of 144 lines, have been recorded for the first time. In the previously reported (J. Mol. Spectrosc.134, 305, 1989; 147, 16, 1991) evaluation of the ATMOS spectrum of CH for determining the molecular parameters we found total interparameter correlations between some of them, due to the absence of high-J lines of the P and Q branches. With the help of the precise constants obtained from our 0-0 band measurements (12 branches with Jmax = 24.5, f = 181, σ = 0.0025 cm−1) of the A2Δ-X2Π transition, we have been able to remove the correlations and obtain more accurate molecular parameters for the X2Π ground state. These constants have subsequently been used to derive new exact molecular parameters for the A2Δ , ν = 1, 2, and 3 levels of CH. The Λ-doubling constants in the A2Δ state were obtained for the first time. The complex vibrational analysis has been carried out to determine the equilibrium molecular constants. Also, RKR potentials and r-centroids have been calculated for both the combining states, as well as Franck-Condon factors for the A-X system.

The High-Resolution ν5 Band of Jet-Cooled Si2F6

Vibration-rotation spectra of the parallel ν5 band of hexafluorodisilane have been measured in a supersonic free jet with 0.001 cm−1 resolution. Three isotopic species, 28,28Si2F6, 28,29Si2F6, and 28,30Si2F6, have been studied. The effect of internal rotation is not observed, indicating that the splitting is smaller than our spectral resolution. A very weak parallel band observed with a slight red shift from the ν5 fundamental band has been assigned tentatively to the (ν4 + ν5)-ν4 hot band.

Spectral simplification by enclosive flow cooling II - diode laser spectroscopy of complex molecules

Molecules with more than four atoms generally exhibit relatively complex vibration-rotation spectra at standard conditions. Often their single lines are not resolved and difficult to detect and investigate by high-resolution absorption spectroscopy. In this work, diode-laser spectroscopic experiments are presented which use the enclosive flow cooling technique for simplification of gas spectra. The fundamental spectral cooling effects on trifluoromethane are compared with theoretical expectations. A considerable reduction of line number density and high optical absorption efficiency were found. Enclosive flow cooling proved to be robust and easy to manage.

Free jet infrared spectroscopy of (28SiF4)2 in the 10 μm region

The rotation–vibration spectra of 28SiF4 dimer have been studied near the ν3 band of monomer 28SiF4. A well-resolved parallel band has been observed 17.5 cm−1 below the monomer band origin. Two perpendicular bands, separated by 2.0 cm−1 and located 4.3 cm−1 above the origin for the lower component, show equidistant Q-branch peaks as only resolved lines. The observed band structure indicates that the threefold degeneracy of the vibrational motions in SiF4 is all removed. A C2h structure with a pair of SiF bonds in an antiparallel position is proposed.

Electric polarity+BrCl–and rotational g factor from analysis of frequencies of pure rotational and vibration–rotational spectra

The electric dipole moment and rotational g factor of BrCl have been estimated by relating non-adiabatic effects, evaluated from analysis of the frequencies of pure rotational and vibration–rotational transitions of BrCl (electronic state X 0+) in its four isotopic variants, to electric and magnetic properties; the electric polarity is +BrCl– and gJ of 79Br35Cl is –0.025 09 ± 0.000 70. Among ten parameters used to reproduce quantitatively 883 frequencies of transitions of four isotopic variants in vibration states up to v= 3, six parameters serve to define the function for potential energy in the range 2.0 < (R/10–10 m) < 2.3; Re=(2.137 037 6 ± 0.000 001 8)× 10–10 m.

The vibration-rotation spectrum and anharmonic potential of H3+

Some qualitative effects of anharmonicity on the spectra of H 3 + and D 3 + between low vibrational levels are described. Using large-basis vibration-rotation calculations with a Morse-based discrete variable representation for the vibrations and a symmetric-top basis for the rotations, new spectra of H 3 + and D 3 + have been assigned. This procedure was assisted by adjusting eight coefficients for H 3 + and six coefficients for D 3 + in the Meyer-Botschwina-Burton ab initio potential function, and eventually 621 new and old lines of H 3 + to levels up to 3 ν 2 and 529 new and old lines of D 3 + to levels up to 2 ν 2 have been fitted with standard deviations of 0.118 and 0.059 cm −1 , respectively. An attempt is made to compare five different potential energy functions for the H 3 + system, two ab initio and three adjusted to fit spectra of H 3 + or D 3 + , by expanding them by the same procedure in the same variables. For extension of the present work to higher vibrational levels, more accurate boundary behaviour at linear configurations will be required, and some aspects of the use of hyperspherical coordinates are discussed.

Vibration–rotational spectra of GaF and molecular properties of diatomic fluorides of elements in group 13

From new measurements of vibration–rotational spectra of 69Ga19F and 71Ga 19F in absorption with laser diodes in the wavenumber region 54 800 ⩽/m–1⩽ 63 800, we evaluated radial coefficients that serve to reproduce the wavenumbers of 229 IR lines and published frequencies of 27 microwave lines within small uncertainties. The maximum range of validity of radial functions is 1.57 ⩽R/10–10 m ⩽ 2.10, and Re=(1.774 341 0 ± 0.000 001 5)× 10–10 m, after corrections for non-adiabatic effects. For comparison with results of GaF and TIF previously reported, we analysed published microwave and IR spectra of BF, AIF and InF; maximum ranges of validity of pertinent radial functions and a table of parameters are presented. For BF we find experimental evidence for the sense –BF+ of electric polarity.

Configurational degeneracy of exchange type in the vibration-rotation spectrum of a nonrigid molecule

In the vibration-rotation spectrum of a nonrigid molecule, the degeneracy that is due to several independent energetically equivalent equilibrium configurations related by exchange transitions is described using the concept of configurational spin. For the CH3OH molecule with three independent configurations related by exchange transitions occurring by internal rotation, the algebraic and symmetric properties of this spin are analyzed, and effective operators of physical quantities are qualitatively constructed based on exchange degeneracy.

Vibration-Rotation Spectra of 13C-Containing Acetylene: The Stretching Fundamentals

High-resolution vibration-rotation spectra of the stretching fundamentals of 13C2H2 and 12C13CH2 have been recorded at Doppler- or pressure-limited resolution in the 8-, 4-, and 3-μm spectral regions. Both cold and hot bands involving stretching and stretching-bending combination levels have been analyzed. The complete treatment of the weak quartic anharmonic resonance between the levels ν3 and ν2 + ν4 + ν5 (Σ+u) in 13C2H2 has been performed, yielding the effective anharmonic constant K2345 and the unperturbed value of the ν3 fundamental for this isotopomer. The analysis of the bands of the 12C13CH2 isotopomer provides values for vibrational energies and rotational constants of the first excited states of all stretching vibrations, including the ν2 = 1 level, not detected before in IR spectra.

Problem of intercollisional correlation in vibration-rotation spectra of molecules

The shapes of vibration-rotation bands are studied considering the statistical dependence between the moments of occurring of different collisions (intercollisional correlation). The expression for the shape of spectral lines has been obtained describing the influence of intercollisional correlation on the absorption in the frequency range near the centers of lines. Modeling of the distribution function for the intervals between adjacent collisions has been carried out. Numerical calculations of the absorption coefficient in the vibration-rotation bands of CO and N 2O have been performed using the proposed model for the line shape. Comparison between calculated results and available experimental data for the absorption at high pressures shows that the present model can adequately explain molecular absorption in compressed gases.

Vibration-rotation spectra of 13C containing acetylene: anharmonic resonances

High resolution vibration-rotation spectra of 13C2H2 were recorded in a number of regions from 2000 to 5200 cm−1 at Doppler or pressure limited resolution. In these spectral ranges cold and hot bands involving the bending-stretching combination levels have been analyzed up to high J values. Anharmonic quartic resonances for the combination levels ν1 + mν4 + nν5, ν2 + mν4 + (n + 2) ν5 and ν3 + (m − 1) ν4 + (n + 1) ν5 have been studied, and the l-type resonances within each polyad have been explicitly taken into account in the analysis of the data. The least-squares refinement provides deperturbed values for band origins and rotational constants, obtained by fitting rotation lines only up to J ≈ 20 with root mean square errors of ≈ 0.0003 cm−1. The band origins allowed us to determine a number of the anharmonicity constants xij0.

Excited states of the molecular ion (H2μ)+

The rotation-vibration spectrum of (H2μ)+ is computed. Radiative lifetimes of the excited states are of order 10−4 s or more. These times can be considered infinite compared to the lifetime ofμ+. For the ion in a crystal the lifetimes are significantly decreased by interaction with polarized molecules of the lattice. Transition rates to the ground state are calculated for (H2μ)+ in a hydrogen crystal. The results make it possible to interpret the experimental data from μSR investigations of hydrogen, deuterium and hydrogen-deuterium mixtures.

Infrared Spectroscopy of HOCl in the 4000-10 000 cm−1 Region

The vibration-rotation spectra of both 35Cl and 37Cl isotopomers of HOCl have been recorded in selected regions between 3900 and 10 500 cm−1 More than 6000 transitions were assigned to the following overtone and combination bands: ν1 + ν3, ν1 + ν2, ν1 + 2ν2, and 3ν1. A Watson-type Hamiltonian in the S reduction and Ir representation was adopted for the analysis, and the vibration-rotation parameters were derived for the excited states. Their values, together with spectroscopic parameters of the fundamental bands reported in the literature, allowed the calculation of a large set of anharmonicity constants and the vibrational dependence of the rotational constants.

Infrared spectroscopy of molecular hydrogen in astrophysical environments

Forty-five years ago Gerhard Herzberg became the first person to observe lines of the infrared rotation–vibration bands of molecular hydrogen; 20 years ago astronomers first found some of these lines in the interstellar medium. Examples are given of astrophysical environments in which H2 has been detected, with emphasis on their growing importance to astronomy. The rotation–vibration spectrum has been observed in emission following both collisional and radiative excitation processes. Recent detections of absorption by cold interstellar molecular hydrogen, both in the gaseous and the solid states, have expanded knowledge of physical properties of molecular clouds and the physical and chemical processes occurring within them.

New observations and analysis of the infrared vibration–rotation spectrum of H3+

The coverage of the infrared spectrum of the [Formula: see text] molecular ion is extended by further measurements of the emission from a small high-pressure hollow-cathode electrical discharge cell, using the pressure-dependence of the intensities to distinguish the lines of [Formula: see text] from the many lies due to electronic transitions of H2 in the same region. The lines were assigned by means of calculations with a large vibration–rotation basis, using a Morse-based discrete variable representation for the vibrations. Eight coefficients in the Meyer–Botschwina–Burton ab initio potential were adjusted in order to fit 621 lines of [Formula: see text] from this and previous work with a standard deviation of 0.118 cm−1.