High-resolution study of the ν1 + ν2 and ν2 + ν3 strongly interacting bands of D2Se

A high-resolution Fourier transform spectrum of the D₂^MSe species (M = 82, 80, 78, 77, and 76) in the region 2300-2500 cm⁻¹ was recorded for the first time and assigned. On the basis of these experimental data, rotation-vibration energies of the (1 1 0) and (0 1 1) vibrational states were fitted, and band centers, and rotational, centrifugal distortion, and resonance interaction parameters were determined for the main D₂⁸⁰Se species. The obtained set of 32 fitted parameters reproduces the 647 rotation-vibration energies with a rms deviation of 0.00024 cm⁻¹. The ν₁ + ν₂ and ν₂ + ν₃ bands of the other four isotopic species are analyzed as well.     

Infrared-microwave double resonance of propynal by using the 3.51 μm HeXe laser

The 3.51 μm HeXe laser is magnetically tuned over a wavenumber of 0.2 cm^?1 and used for infrared absorption and double resonance spectroscopy. Eight rotation-vibration lines of propynal in the ν₂ band are assigned by the Stark effect. Eleven microwave transitions in the v₂ = 1 vibrational state are observed by the method of infrared-microwave double resonance. The rotational constants of the excited state and the band origin of the vibration ν₂ are determined from the observed spectra.     

Microwave spectrum of silyl fluoride: Coriolis resonance between ν2 and ν5 states

The J = 1 ← 0 and J = 2 ← 1 microwave rotational transitions of SiH₃F and SiD₃F have been measured for the ground and the v₂ = 1, v₃ = 1, v₅ = 1, and v₆ = 1 vibrational states, for which the various rotational and vibration-rotation interaction constants have been obtained. Both molecules show an X-Y Coriolis resonance between the ν₂ and ν₅ vibrational states, whose separation are 29 and 8 cm^?1, respectively. In the case of SiD₃F the resonance is very strong and an exact numerical diagonalization of the energy matrix was employed.     

Line positions and energy levels of the O substitutions from the HDO/D2O spectra between 5600 and 8800 cm

Absorption spectra of HDO/D₂O mixtures recorded in the 5600-8800 cm⁻¹ region with a total pressure of water from 13 up to 18 hPa and an absorption path length of 600 m have been analyzed in order to obtain new spectroscopic data for HD¹⁸O and D₂¹⁸O. In spite of the low natural ¹⁸O concentration (about 2×10⁻³ with respect to the ¹⁶O one), about 1100 transitions belonging to HD¹⁸O and more than 280 transitions belonging to D₂¹⁸O have been assigned. Most of the D₂¹⁸O transitions belong to the ν₁+ν₂+ν₃ and 2ν₁+ν₃ bands. Sets of energy levels for seven vibrational states of D₂¹⁸O and four states of HD¹⁸O are reported for the first time. The comparison of the experimental data with the calculated values based on Partridge-Schwenke global variational calculations is discussed.     

The interacting states (020), (100), and (001) of H217O and H218O

A fit of about 350 rotational levels of the (020), (100), and (001) vibrational states has been performed for H₂¹⁷O as well as for H₂¹⁸O leading to the determination of 51 rotational and coupling constants for each isotopic species. The Fermi-type interaction and the two Coriolis-type interactions have been taken into account by appropriate rotation-vibration operators and the v-diagonal part of the Hamiltonian is, for each vibrational state, a Watson-type Hamiltonian. The results are very satisfactory since 87% of the experimental levels are reproduced within 15 × 10^?3 cm^?1.     

A new Morse-oscillator based Hamiltonian for H3+: Calculation of line strengths

In two recent publications [V. Špirko, P. Jensen, P. R. Bunker, and A. Čejchan, J. Mol. Spectrosc. 112, 183–202 (1985); P. Jensen, V. Špirko, and P. R. Bunker, J. Mol. Spectrosc. 115, 269–293 (1986)], we have described the development of Morse oscillator adapted rotation-vibration Hamiltonians for equilateral triangular X₃ and Y₂X molecules, and we have used these Hamiltonians to calculate the rotation-vibration energies for H₃⁺ and its X₃⁺ and Y₂X⁺ isotopes from ab initio potential energy functions. The present paper presents a method for calculating rotation-vibration line strengths of H₃⁺ and its isotopes using an ab initio dipole moment function [G. D. Carney and R. N. Porter, J. Chem. Phys. 60, 4251–4264 (1974)] together with the energies and wave-functions obtained by diagonalization of the Morse oscillator adapted Hamiltonians. We use this method for calculating the vibrational transition moments involving the lowest vibrational states of H₃⁺, D₃⁺, H₂D⁺, and D₂H⁺. Further, we calculate the line strengths of the low-J transitions in the rotational spectra of H₃⁺ in the vibrational ground state and in the ν₁ and ν₂ states. We hope that the calculations presented will facilitate the search for further rotation-vibration transitions of H₃⁺ and its isotopes.     

High-resolution rovibrational analysis of vibrational states of A2 symmetry of the dideuterated methane CH2D2: the levels ν 5 and ν 7 + ν 9

The infrared spectrum of the CH₂D₂ molecule has been measured in the region 900–1500?cm^?1 on a Bomem DA002 Fourier transform spectrometer with a resolution of 0.0024?cm^?1 (FWHM, unapodized). Transitions belonging to the hot bands ν ₇?+?ν₉?ν ₇, ν₇?+?ν₉? ν ₉, ν₅?+?ν₇?ν₅, and ν₅?+?ν₉?ν₅ were extracted from the recorded spectra to determine the rovibrational energies of the A₂ symmetry vibrational states (v ₇?=?v ₉?=?1) at 2329.698?cm^?1 and (v ₅ ?=?1) at 1331.409?cm^?1. Vibrational energies as well as rotational and centrifugal distortion parameters of the (v ₇?=?v ₉=1) and (v ₅?=?1) states were determined that reproduce the experimental rovibrational energy levels of the (v ₇?=?v ₉?=?1) and (v ₅?=?1) vibrational states with a d _rms deviation of 0.0017 and 0.0006?cm^?1, respectively. The results are discussed in relation to the equilibrium structure of methane, which is redetermined here from the experimental data, and in relation to its potential hypersurface and anharmonic vibrational dynamics.     

Carbon suboxide as a quasilinear molecule with a large amplitude bending mode: Determination of the molecular constants and the ν7 potential function

The model of a quasilinear molecule with a large amplitude bending mode is used to treat C₃O₂. The Hamiltonian operator, including the rotation-vibration interaction, is derived allowing only a single vibrational degree of freedom, namely, the ν₇ mode corresponding to the bending at the central carbon atom. The CCO angle is constrained to be 180°. With this model the rotational energy levels and, thus, the molecular constants can be computed for any ν₇ level once the ν₇ potential is specified. The l-doubling is included only for π states. The model contains three adjustable parameters: the rotational constant in the linear configuration and two terms in the potential function, and these are determined by fitting three experimental quantities: the rotational constants in and the separation between the ground and 2ν7⁰ states. The resulting ν₇ potential has a 30.56 cm^?1 barrier at α = 0 with a minimum at α = 11.04°, where 2α is the angular deviation from linearity. The model gives a good fit to the 2ν₇ Raman data and to the rotational and centrifugal distortion constants in all of the nν7^l states which have been analyzed. A similar analysis is applied with equal success to the states with ν₄, the asymmetric CC stretch mode at 1587 cm^?1, simultaneously excited with a ν₇ mode. The potential in this case has a 56.58 cm^?1 barrier at α = 0 with a minimum at α = 13.02°.     

Microwave spectrum of silicon difluoride in the excited vibrational states,equilibrium structure,anharmonic potential function,and ν1-ν3 Coriolis resonance

The microwave spectrum of SiF₂ was identified in the excited states of the stretching vibrations. It was found that the Coriolis resonance between the v₁ = 1 and v₃ = 1 vibrational states has perturbed very much the spectra of these states. An extensive analysis of the Coriolis resonance gave a very accurate value of the difference between the ν₁ and ν₃ fundamental frequencies, ν₁ - ν₃ = ? 15.395 ± 0.001 cm^?1 and, thus, gave a strong basis to the assignment of the stretching modes by Khanna et al. An intervibrational-state transition, v₁ = 1, 8₅₄ ← v₃ = 1, 8₁₇ was identified.The observed rotational constants in the v₁ = 1 and v₃ = 1 states were combined with those in the ground and v₂ = 1 states by Rao and Curl to obtain the equilibrium structure, harmonic force constants and complete sets of the cubic and the third-order potential constants.     

Joint Rotational Analysis of 16 Vibrational States of HDSe

High-resolution Fourier transform spectra of HD⁸⁰Se in the region of the ν₁+ν₃, 2ν₂+ν₃, 2ν₁+ν₂, 3ν₁, and ν₂+2ν₃ absorption bands, with centers located between 4000 and 5500 cm⁻¹, were recorded and rovibrationally analyzed. Energies of the (101), (021), (210), (300), and (012) states, together with those of the formerly reported (010), (100), (020), (001), (120), (110), (030), (011), (200), (002), and (003) states, were jointly used as input information in a “global fit” procedure. This fit provided 161 spectroscopic parameters which reproduce 3323 observed energies with accuracies close to experimental uncertainties. These parameters are compared with those predicted from H₂Se. Moreover, experimental band centers for HSeD are compared with those calculated theoretically.     

Joint ro-vibrational analysis of the HDS high resolution infrared data

High resolution Fourier transform spectra of the HDS molecule were recorded and analyzed for the first time in the region of the bands ν₁ + 2ν₂ (3938.6 cm⁻¹), ν₁ + ν₃ (4522.6 cm⁻¹), 2ν₂ + ν₃ (4638.8 cm⁻¹), 2ν₁ + ν₂ (4767.7 cm⁻¹), ν₁ + ν₂ + ν₃ (5525.2 cm⁻¹), 3ν₁ (5560.6 cm⁻¹), ν₁ + 2ν₃ (7047.2 cm⁻¹), and 2ν₂ + 2ν₃ (7123.9 cm⁻¹). The ro-vibrational energies of the upper vibrational states of these bands together with the ro-vibrational energies of 12 other bands already studied at high resolution were used as inputs in a Global Fit analysis firstly described in [O.N. Ulenikov, G.A. Onopenko, H. Lin, J.-H. Zhang, Z.-Y. Zhou, Q.-S. Zhu, R.N. Tolchenov, J. Mol. Spectrosc. 189 (1998) 29-39]. In this case, the resonance interactions between the states (v₁v₂v₃) and (v₁ ± 2 v₂ ? 1 v₃ ? 1) were taken into account. The resulting set of 143 parameters reproduces all the experimental data (2984 vibration-rotation energies of 20 vibrational states which correspond to about 9700 ro-vibrational transitions with J^max = 23) with accuracies comparable with the experimental uncertainties.     

Diode laser spectrum of diacetylene near 5 μm

The ν₅ rotation-vibration fundamental band and the ν₅ + ν₉ band of diacetylene in the region 2000–2037 cm^?1 have been measured to an accuracy of better than ±0.004 cm^?1 using a tunable-diode laser spectrometer. The l-type doubling in the (ν₅ + ν₉ ? ν₉ band has been resolved. Line positions, assignments, band origins, and rotational constants B′_v, B″_v, D′_v, and D″_v are reported.     

Torsional tunneling splittings in the v4 = 1 excited torsional state of Si2H6: analysis of hot bands accompanying fundamental transitions in the high resolution infrared spectrum

The (ν₄?+?ν₆)???ν₄, (ν₄?+?ν₈)???ν₄ and (ν₄?+?ν₉)???ν₄ hot infrared systems of disilane (Si₂H₆) have been analysed at high resolution, and the values of the relative vibration–rotation–torsion parameters have been determined. The torsional splitting is about 0.500?cm^?1 in the ν₄ and ν₄?+?ν₆ states, and decreases strongly in the vibrationally degenerate upper states ν₄?+?ν₈ (about 0.0272?cm^?1 on average) and ν₄?+?ν₉ (about 0.3019?cm^?1), consistent with theoretical predictions. Comparison between the vibrational wavenumbers of cold transitions and hot transitions originating in the excited torsional state v₄?=?1 allows one to determine the change of the fundamental torsional frequency ν₄ caused by the excitation of small amplitude vibrations. A remarkable increase in ν₄ of about 8.599?cm^?1 is found in the v₉?=?1 state (E_1d SiH₃-rocking mode, asymmetric to inversion in the staggered geometry), and this corresponds to an increase in the torsional barrier height in this excited fundamental vibrational state by about 48.77?cm^?1. The mechanism responsible for the decrease of the torsional splittings in the degenerate vibrational states is briefly outlined by means of second-order perturbation theory, using torsion-hindered vibrational basis functions of E_1d and E_2d symmetries for the degenerate modes.     

Simultaneous analysis of the ν1, ν4, 2ν2, ν2 + ν5, and 2ν5 infrared bands of 12CH3F

The Fourier-transform spectrum of CH₃F from 2800 to 3100 cm^?1, obtained by Guelachvili in Orsay at a resolution of about 0.003 cm^?1, was analyzed. The effective Hamiltonian used contained all symmetry allowed interactions up to second order in the Amat-Nielsen classification, together with selected third-order terms, amongst the set of nine vibrational basis functions represented by the states ν₁(A₁), ν₄(E), 2ν₂(A₁), ν₂ + ν₅(E), 2ν₅⁰(A₁), and 2ν₅^±2(E). A number of strong Fermi and Coriolis resonances are involved. The vibrational Hamiltonian matrix was not factorized beyond the requirements of symmetry. A total of 59 molecular parameters were refined in a simultaneous least-squares analysis to over 1500 upper-state energy levels for J ≤ 20 with a standard deviation of 0.013 cm^?1. Although the standard deviation remains an order of magnitude greater than the precision of the measurements, this work breaks new ground in the simultaneous analysis of interacting symmetric top vibrational levels, in terms of the number of interacting vibrational states and the number of parameters in the Hamiltonian.     

The vibration-rotation problem in triatomic molecules allowing for two large-amplitude stretching vibrations

An expression for the Hamiltonian of a vibration-rotating triatomic molecule is derived, using two curvilinear stretching coordinates ?₁ and ?₃ and one rectilinear bending coordinate S₂, in such a way that the Hamiltonian obtained is applicable to any bent triatomic molecule and allows for large displacements along the stretching coordinates. From this, a zeroth-order Hamiltonian H_s⁰ (?₁, ?₃) is obtained, describing the energy levels associated with the two stretching vibrations ν₁ and ν₃. The vibrational energy levels (v₁, v₃^even) of an XY₂ molecule having unequal bond lengths at equilibrium are then calculated. The kinetic energy T₀ (?₁, ?₃) of the Hamiltonian effectively takes into account the two large-amplitude motions in ν₁ and ν₃ together with their interaction. A model calculation is described for a bent XY₂ molecule (SO₂ in its ¹A′ (¹B₂) excited state) in which the ν₃ oscillation occurs in a double-minimum potential. Coupling by kinetic energy terms in the Hamiltonian turns out to be very small in this example.     

Vibration-rotation energies of harmonic and combination levels in tetrahedral XY4 molecules: Analysis of the 2ν2 and ν2 + ν4 bands of 12CH4

The theory and the extrapolation method described in the previous paper are used to analyze the v₂ = 2 and v₂ = v₄ = 1 levels of ¹²CH₄. In addition to the well-known parameters of the ground, v₂ = 1, and v₄ = 1 states, the computation of energy levels involves only 6 new parameters for 2ν₂ and 13 for ν₂ + ν₄ up to the fourth order of approximation. These parameters have been determined from Raman and infrared data. Forty-four Raman lines observed by Berger in the region from 3060 to 3090 cm^?1 have been assigned to the 2ν₂ band. The standard deviation obtained by fitting 39 of these transitions with the 6 corresponding parameters is 0.025 cm^?1. The calculated frequencies of ν₂ + ν₄ are compared with moderate resolution ir spectra recorded in our laboratory and the recent spectra of Hunt et al. Totally polarized weak Raman lines observed by Berger in the region from 2850 to 2900 cm^?1 have been assigned to the ν₂ + ν₄ band arising through a second-order Coriolis interaction with the ν₁ band. A project of a comprehensive treatment of the energy levels of methane between 2550 and 3650 cm^?1 is discussed.     

ν7 and ν9 bands of formic acid near 16 μm

The ν₇ and ν₉ fundamental bands of formic acid were studied by Fourier transform spectroscopy with a resolving power of 0.020 cm^?1. Band centers obtained are ν₇ = 626.158 cm^?1 and ν₉ = 640.722 cm^?1. It was possible to determine rotational and centrifugal distortion parameters for both vibrational states v₇ = 1 and v₉ = 1 and also the two first-order Coriolis interaction parameters along z and x axes and the second-order Coriolis parameter along z axis. The stability of rotational and distortion parameters compared to ground state values confirms that a Watson type Hamiltonian is well adapted to such a problem.     

Global fit of the high-resolution infrared spectrum of D2S

High-resolution Fourier-transform spectra of the D₂S molecule in the regions of polyads of interacting vibrational states v = 3/2, 2, 5/2, 3 and 7/2 (v = v₁ + v₂/2 + v₃) were recorded for the first time with a Bruker IFS 120 Fourier-transform interferometer and analysed. A global fit of all currently available rotation-vibration energies has been made for 22 vibrational states of the D₂S molecule. The resulting set of 231 parameters reproduces all the initial experimental data (about 3670 vibration-rotation energies which correspond to more than 9700 ro-vibrational transitions with J^max = 25) with accuracies close to the experimental uncertainties.     

On the study of high-resolution rovibrational spectrum of H2S in the region of 7300-7900 cm

High-resolution Fourier transform infrared spectrum of H₂S was recorded and analyzed in the region of the v=v₁+v₂/2+v₃=3 poliad. Experimental transitions were assigned to the 3ν₁, 2ν₁+ν₃, ν₁+2ν₃, 3ν₃, 2ν₁+2ν₂, and ν₁+2ν₂+ν₃ bands with the maximum value of quantum number J equal to 11, 14, 10, 11, 8, and 11, respectively. The theoretical analysis was fulfilled with the Hamiltonian model which takes into account numerous resonance interactions between all the mentioned vibrational states. The rms deviation of the reproduction of 510 upper energy levels (derived from more than 1550 transitions) with 75 parameters was 0.0022 cm⁻¹.     

The ν2 and ν4 bands of AsH3

The infrared absorption of arsine, AsH₃, between 750 and 1200 cm^?1 has been recorded at a resolution of 0.006 cm^?1. Altogether 2419 transitions, including nearly 700 “perturbation allowed” transitions with Δ∥k ? l∥ = ±3, ±6, and ±9, have been assigned to the ν₂(A₁) and ν₄(E) bands. Splitting of the transitions for K″ = 3, 6, and 9 was also observed. To fit the rotational pattern of the v₂ = 1 and v₄ = 1 vibrational states up to J = 21, all the experimental data were analyzed simultaneously on the basis of a rovibrational Hamiltonian which took into account the Coriolis interaction between ν₂ and ν₄ and also included several essential resonances within them. The derived set of 38 significant spectroscopic parameters reproduced the 2328 transition wavenumbers retained in the final fit within the accuracy of the experimental measurements.