Local Mode Pair Research Articles

The absorption spectrum of H 2S between 9540 and [formula omitted] by intracavity laser absorption spectroscopy with a vertical external cavity surface emitting laser

An Intracavity Laser Absorption Spectrometer (ICLAS) based on a Vertical External Cavity Surface Emitting Laser (VECSEL) has been used to record the absorption spectrum of H 2S between 9540 and 10 000 cm −1 with pressures up to 122 Torr (160.5 hPa) and equivalent absorption path lengths up to 45 km. More than 1600 absorption lines were attributed to the transitions reaching the highly excited (40 ±,0), (30 ±,2), and (11 +,4) states (local mode notation). The existing information relative to the (40 ±,0) local mode bright pair at 9911.02 cm −1 was considerably enlarged, while the other states are reported for the first time. Eight hundred and ninety two precise energy levels were derived, including 181 and 28 levels for the H 2 34 S and H 2 33 S minor isotopomers, respectively. These energy levels were fitted using a Watson-type rotational Hamiltonian and the spectroscopic parameters were obtained, yielding an rms deviation of 0.006 cm −1 for the H 2 32 S species—close to the experimental accuracy. The dark states—(20 +,4) and (11 +,4)—at 9647.77 and 9744.88 cm −1 , respectively, were found to perturb the observed energy levels and were then included into the final energy levels modeling. The (40 ±,0) states are very close to the local mode limit, i.e., with a mostly identical rotational structure. The (30 ±,2) states are separated by 0.077 cm −1 and this separation holds for most of the rotational sublevels. The resonance interactions between the three local mode pairs—(40 ±,0), (30 ±,2), and (20 ±,4)—and the (11 +,4) state affect in some cases specifically one of the component of the pair and then the energy separation of the corresponding near degenerate rotational levels. Line intensities were obtained on the basis of the relative intensities measured by ICLAS and from absolute values of the stronger lines measured separately by Fourier Transform Spectroscopy associated with a multipass cell. The transition intensities could be successfully modeled and the integrated band intensities are given and discussed.

H232S : First Observation of the (70±,0) Local Mode Pair and Updated Global Effective Vibrational Hamiltonian

The absorption spectrum of H2S has been recorded by intracavity laser absorption spectroscopy in the spectral region 16 180–16 440 cm−1 corresponding to an excitation of the (70±, 0) local mode pair. Seventy-seven sublevels could be rotationally assigned and fitted with a rms of 0.009 cm−1 by considering the (70±, 0) local mode pair as isolated. The corresponding vibrational terms combined with all the levels reported in the literature were used to refine the effective vibrational Hamiltonian parameters of H232S. The importance of the Fermi-type interaction is discussed.

Local Mode Effects in the Absorption Spectrum of H2S between 10 780 and 11 330 cm−1

The absorption spectrum of H2S (1159 lines) has been recorded between 10 780 and 11 330 cm−1 by intracavity laser absorption spectroscopy (ICLAS). As a result of the increase of sensitivity of ICLAS over previous Fourier transform investigations in the same spectral region, the number of experimental energy levels of the (40+, 1) and (40−, 1) local mode states ((212) and (311) in normal mode notation) has been triplicated for the main isotopic species H232S (198 compared to 62). Moreover, 112 energy levels of H234S and 25 energy levels of H233S, present in natural abundance in the sample, could also be determined. Three rotational levels of the (30±, 3) local mode pair of dark states ((132) and (231) in normal mode notation) of H232S could also be observed through extra lines borrowing their intensities via resonance interactions with line-partners of the dominant bands. The (40+, 1) and (40−, 1) local mode states form a degenerate local mode pair, with the same rotational structure for the two components. The observed energy levels were reproduced by an effective Hamiltonian including the (40±, 1) and (30±, 3) interacting local mode pairs. This Hamiltonian was applied either in the C2v or Cs symmetry groups leading to an rms deviation of 0.0058 and 0.0068 cm−1 respectively, comparable to the experimental accuracy (0.0028 cm−1). The degeneracy of the rotational structure of the (40±, 1) pair is unaffected by the interaction with the nearby (30±, 3) local mode states. On the contrary, an additional interaction with dark states lifts in some cases this degeneracy. The same effective Hamiltonian with scaled parameters was success fully used to reproduce the energy levels of the H233S and H234S isotopic species. Finally, the extremely weak 3ν1+3ν2 band of H232S at 11 097.161 cm−1 could also be detected leading to the determination of 70 levels of the corresponding (21+, 3) upper state ((330) in normal mode notation). The integrated intensities have been estimated for the bands corresponding to the (40+, 1) and (40−, 1) upper states. A total of six transformed dipole moment parameters were derived from the measured line intensities allowing to simulate very satisfactorily the observed spectrum. The transition moment relative to the (40−, 1) upper state is found about twice as large as the one relative to the (40+, 1) state.

Calculations of stretching vibrational energy levels of the CH 3 I molecule by a nonlinear model

A nonlinear model, i.e. the quantized discrete self-trapping equation, is applied to calculate the highly excited CH stretching vibrational energy levels of the CH3I molecule in the liquid phase at the electronic ground state up to n=8. The obtained results agree well with the experimental data and with those obtained from local mode model calculations. We note that the dominant feature of the methyl CH stretching vibrational energy levels of the CH3I molecule is a pattern of local mode pairs. When n≥7, all the vibrational energy of the CH3 group can nearly be localized on a single CH bond.

High-resolution spectroscopic study of H2 80 Se in the ν(stretch) = 5 and 6 local-mode pairs states

High-resolution spectra of the H2 80Se molecule (50±,0), A1/B2 and (60±,0), A1/B2 (local mode pairs) stretching states were recorded using a Fourier transform spectrometry technique and also a Ti: sapphire laser photo-acoustic spectrometer with resonance cavity and multi-pass cell. The vibrational wavefunction, stretching band origins, rotational constants and Coriolis coefficients of H2 80Se molecule ν = 5 and 6 local-mode pairs were calculated by using the NMDD (normal mode with Darling—Dennison resonance included) model. These parameters were used to predict the upper state energy levels, which were used as the bases of ground state combination differences for assigning the vibration—rotational transitions of H2 80Se molecule ν = 5 and 6 local-mode pairs states. Several striking local-mode limit effects and the formation of four-fold ro-vibrational energy clusters were observed and discussed.

High-resolution spectroscopic study of H2 80Se in the nu (stretch) = 5 and 6 local-mode pairs states

High-resolution spectroscopic study of H2 80Se in the nu (stretch) = 5 and 6 local-mode pairs states

The Overtone Spectrum of H2 32S near 13 200 cm−1

The intracavity laser absorption spectrum of H232S has been recorded near 13200 cm−1with an equivalent absorption pathlength of 25 km. The observed spectrum is assigned to the (50±,v2= 1) states constituting a local mode pair in strong H22-type interaction. The rovibrational analysis has allowed the assignment of 210 lines involving 86 rotational upper state levels which have been reproduced with a rms of 0.023 cm−1close to the experimental accuracy. A perturbation affecting one line is assigned to a local interaction with the (40±,v2= 3) local mode pair. The influence of the bending excitation on the local mode character of the (n0±,v2= 1) stretch-bend combination levels is discussed on the basis of the values of the rotational constants and of the H22interaction parameters.

The H2S Spectrum around 0.7 μm

The overtone spectrum of H2S has been recorded by intracavity laser spectroscopy in the 14100–14400 cm−1spectral region. The rovibrational analysis was performed allowing one to assign not only lines involving the pair of interacting states {(402), (303)} ({(60+, 0), (60−, 0)} in local mode notation), but also lines involving the interacting states {(322), (223)} ({50+, 2), (50−, 2)} in local mode notation). Indeed, apart from the strong H22interactions that link the rotational levels of the states (60±, 0) on the one hand, and the rotational levels of the states (50+, 2) on the other hand, we observe that the rotational levels of the two pairs of states interact strongly through anharmonic and Coriolis-type resonances. These resonances transfer intensity to lines involving the (50+, 2) pair of states. Altogether 80 rotational upper-state levels have been observed and reproduced satisfactorily using an Hamiltonian matrix that takes explicitly into account the various interactions and assumes the same vibrational energy and rotational constants for the two components of the local mode pairs. The following band centers have been obtained: ν0(60+, 0) = 14291.122 cm−1and ν0(50±, 2) = 14284.705 cm−1. Finally a local mode-type behavior is evidenced by the values of the Hamiltonian constants, and refined vibrational local mode parameters are obtained.

Calculations of stretching vibrational overtones and combinations of arsine by nonlinear model

A three-parameter nonlinear model in nonlinear quantum theory, i. e., the quantized discrete self-trapping equation, has been used to calculate the vibrational energy spectrum, including the overtones and combinations with many excited quanta, of AsH stretches of arsine, AsH3. The model calculations agree well with experiment and other calculations. It is shown that the dominant feature of the energy spectrum of AsH3 molecule is a pattern of local mode pairs, and that when n ≥ 4, all the vibrational energies are almost localized on a single AsH bond.

High resolution spectroscopic study of H2Se (40+,0) A1 and (40-, 0) B2 stretching states: normal mode and local mode analysis

High resolution spectra of the coupled and degenerate (40+, 0) A1 and (40-, 0) B2 (the local mode pair) states of H2Se are reported. The vibration–rotation transitions of H2 n Se (n = 80,78) were assigned by using the ground state combination differences and least-squares fits to yield the rotational and coupling constants for the two stretching states with degenerate band origins: υ0 (40+, 0) = 8894·504cm-1; υ0 (40-, 0) = 8894·504cm-1. Several striking local 0 0 mode limit effects and the formation of fourfold rovibrational energy clusters are observed and discussed.

High resolution spectroscopic study of H2 Se (40+,0) A1 and (40-,0) B2 stretching states: normal mode and local mode analysis

High resolution spectra of the coupled and degenerate (40+, 0) A1 and (40-, 0) B2 (the local mode pair) states of H2Se are reported. The vibration–rotation transitions of H2 n Se (n = 80,78) were assigned by using the ground state combination differences and least-squares fits to yield the rotational and coupling constants for the two stretching states with degenerate band origins: υ0 (40+, 0) = 8894·504cm-1; υ0 (40-, 0) = 8894·504cm-1. Several striking local 0 0 mode limit effects and the formation of fourfold rovibrational energy clusters are observed and discussed.

High resolution photoacoustic spectrum of AsH 3 ( [formula omitted]) bands

The high resolution spectrum of arsine in the region of 11 470-11 650 cm −1 was recorded by a sensitive laser photoacoustic apparatus. The vibration-rotation transitions of the local mode pair of bands ( 600A 1 E ) were assigned and their major vibration-rotation parameters were obtained by least-square fitting. The results indicate that the selection rules on the quantum number k have no effect in the high J values owing to strong Coriolis coupling. In addition, the intensities of vib-rotational transitions were estimated by comparison with standard water lines.

Local Mode Effects on the High-Resolution Overtone Spectrum of H2S around 12 500 cm−1

The overtone spectrum of H2S has been studied by intracavity laser absorption spectroscopy in the wavenumber region 12 270–12 670 cm−1. The rovibrational analysis has provided upper state rotational parameters for the three interacting vibrational states, (401), (104), and (024), observed in the region. The rotational levels of the first two states, constituting the local mode pair 41±, are strongly coupled by a strongH22type interaction. The (024) state is observed via a local perturbation. Altogether, 399 rovibrational lines have been assigned, including 172 rotational upper state sublevels which have been reproduced calculationally within the experimental accuracy of 0.015 cm−1. A local mode type behavior is evidenced by the values of the rotational parameters.

Fermi resonances and local modes in stibine, SbH3: A Fourier interferometric and laser photoacoustic study of the overtone spectrum

The third stretching overtone region of a natural sample of stibine, SbH3, has been studied with high resolution infrared spectroscopy and the fifth and the sixth overtone region with Ti:Sapphire ring laser intracavity photoacoustic spectroscopy. The third overtone consists of a local mode pair of bands (400A1/E) which have been rotationally assigned both for 121SbH3 and 123SbH3 with a vibration-rotation model based on rectilinear normal coordinates. The vibrational dependencies of the model parameters are explained well with a simple block diagonal vibrational model. An extension of the standard vibration-rotation model is used to show that the upper state rotational energy level structures of both isotopic species are close to the rotational structure of an asymmetric rotor. High resolution laser spectrum of the fifth overtone consisting of a local mode pair of bands (600A1/E) shows severe perturbations in the upper state rotational structure. The (510A1/E) and (700A1/E) bands have been recorded with low resolution. All experimentally known vibration-rotation band origins of 121SbH3 have been reproduced well with a curvilinear internal valence coordinate system based Fermi resonance local mode model. The potential energy surface obtained agrees well with recent ab initio results.

An analytic semiclassical model for local and normal stretching modes in AB 2 molecules

We present a simple, analytic model for the normal and local mode behavior of the stretching vibrations in AB 2 molecules. Starting with a zeroth-order description of degenerate, harmonic normal modes, we introduce a quartic perturbation and employ first-order secular perturbation theory to obtain a closed-form expression for the Poincaré surface of section for the action-angle variable pair corresponding to the vibrational angular momentum. Local modes correspond to pairs of levels trapped below a dynamical barrier along this angle variable; normal modes, to levels above the barrier. Uniform semiclassical quantization completely lifts the degeneracy of the zeroth-order states, and predicts the appropriate trends in the ordering of the various modes and the splitting between local mode pairs.