E.S. Bekhtereva

Analysis of highly excited ‘hot’ bands in the SO2 molecule: ν2 + 3ν3 − ν2 and 2ν1 + ν2 + ν3 − ν2

We set up a variational procedure of assignments of transitions and we applied it to the analysis very weak ‘hot’ bands, ν2 + 3ν3 − ν2 and 2ν1 + ν2 + ν3 − ν2, of the SO2 molecule. As the first step of the study, the ‘cold’ bands, 3ν3 and 2ν1 + ν3, are re-analysed and transitions belonging to those bands are assigned up to the values of quantum numbers J max. = 60, , and J max. = 69, for the bands 3ν3 and 2ν1 + ν3, respectively. After ‘cleaning’ the experimental spectrum from transitions belonging to the 3ν3 and 2ν1 + ν3 bands, a variational procedure was used that allowed us to assign 230 and 115 transitions with the values of quantum numbers J max. = 35, , and J max. = 26, for the bands ν2 + 3ν3 − ν2 and 2ν1 + ν2 + ν3 − ν2, respectively. The sets of spectroscopic parameters obtained by fitting the assigned experimental transitions reproduce the initial experimental data with an accuracy close to experimental uncertainties.

High resolution vibration-rotation spectrum of the D2O molecule in the region near the 2ν1 + ν2 + ν3 absorption band

The high resolution Fourier transform spectrum of the D20 (ν = ν1 + ν2/2 + ν3 = 3.5) polyad was analysed within the framework of the Hamiltonian model taking into account resonance interactions between the seven states (310), (211), (112), (013), (230), (131) and (032). Transitions belonging to the 2ν1 + ν2 + ν3, 3ν1 +ν2 and 3ν2 + 2ν3 bands were assigned in the experimentally recorded spectrum. This provided the possibility of obtaining spectroscopic parameters of the ‘visible’ states (211), (310) and (032) and of estimating the band centres, and the rotational and resonance interaction parameters of the ‘dark’ states (112) and (131).

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.

High resolution study of the ν5 + ν12 band of C2H4

The combination band ν5 + ν12 of ethylene, C2H4, has been recorded for the first time with a high resolution Fourier transform spectrometer Bruker IFS 125HR. Assignments of transitions and preliminary rotational analysis are made. Two models (Hamiltonian of the isolated vibrational state and Hamiltonian that takes into account resonance interactions) are used. Influence of the local resonance interactions on the parameters and reproduction power of the models is discussed.

High resolution Fourier transform spectroscopy of CH2D2 in the region 2350–2650 cm−1: the bands ν5+ν7, 2ν9, ν3+ν4, ν3+ν7 and ν5+ν9

The IR spectrum of the CH2D2 molecule has been measured in the region of 2350–2650 cm−1 on a Bomem DA002 Fourier transform spectrometer with a resolution of 0.004 cm−1 (FWHM, apodized) and analyzed with a Hamiltonian model which takes into account resonance interactions between all vibrational states in that region. More than 3000 transitions have been assigned to the bands 2ν9, ν3 + ν4, ν5 + ν9, ν5 + ν7 and ν3 + ν7 using ground state combination differences from the known ground state parameters. A set of 115 spectroscopic parameters for the excited vibrational states is obtained from a least squares adjustment. This reproduces the 646 initial upper ro-vibrational energies used in the fit with a drms = 0.0036 cm−1.

On the ‘expanded local mode’ approach applied to the methane molecule: isotopic substitutions CH3D ←CH4 and CHD3 ←CH4

Operator perturbation theory and the symmetry properties of the axially symmetric XYZ3 (C3v) type molecules are used for the determination of the spectroscopic parameters in the form of functions of structural parameters and parameters of the intramolecular potential function. Several relations between sets of spectroscopic parameters of these molecules are obtained. The ‘expanded local mode’ model and the general isotopic substitution theory are used to estimate the relations between spectroscopic parameters of CH3D and CHD3, on one hand, and with the Td symmetric isotopic species, CH4, on the other hand. Test calculations with the isotopic relations show that even without including prior information about the CH3D and CHD3 species, numerical results of calculations are in a good agreement both with experimental data and with results of ab initio calculations.

On the ‘expanded local mode’ approach applied to the methane molecule: isotopic substitution CH2D2 ←CH4

On the basis of a compilation of the ‘expanded local mode’ model and the general isotopic substitution theory, sets of simple analytical relations between different spectroscopic parameters (harmonic frequencies, ωλ, anharmonic coefficients, x λμ, ro-vibrational coefficients, , different kinds of Fermi- and Coriolis-type interaction parameters) of the CH2D2 molecule are derived. All of them are expressed as simple functions of a few initial spectroscopic parameters of the mother, CH4, molecule. Test calculations with the derived isotopic relations show that, in spite of a total absence of initial information about the CH2D2 species, the numerical results of the calculations have a very good correlation both with experimental data, and results of ab initio calculations.

High-resolution spectrum of the , and ν3+ν4(A2) bands of the PH3 molecule: assignments and preliminary analysis

Abstract The high-resolution (0.005 cm −1 ) Fourier transform infrared spectrum of PH3 is recorded in the region between 3280 and 3580 cm −1 where the following bands are located: ν 1 +ν 4 (E), ν 3 +ν 4 (E), ν 3 +ν 4 (A 1 ) , forbidden on symmetry band ν3+ν4(A2), and very weak bands ν 1 +ν 2 (A 1 ), ν 2 +ν 3 (E) . Transitions are assigned to the first four ones. Vibrational analysis of known experimental data is made.

On the local mode behaviour of the XH2/XD2 and XD/XH fragments with respect to the deuterated species of the near local mode XH3(C3v ) molecule

Effect of isotopic substitution in the near local mode, XH3(C3v ), molecules is considered. On that basis it is shown that the spectroscopic properties of deuterated and/or di-deuterated isotopic species of the XH3(C3v ) molecule with the value of interbond angle close to π/2 are analogous to the spectroscopic properties of its separate fragments: of a three-atomic local mode ‘molecule’ XH2/XD2 and of a diatomic XD/XH ‘molecule’. The phosphine molecule is considered as an illustration.

Rovibrational analysis of the ν2 and 2ν2 P–D stretching bands of PH2D

Abstract The infrared spectral regions of the P–D stretching fundamental band ν2 and the first overtone band 2ν2 of PH2D were recorded with a resolution of 2.7×10−3 and 6.8×10 −3 cm −1 , respectively. In the analysis about 710 and 440 transitions were assigned to the ν2 and 2ν2 bands. These provided 358 and 268 upper rovibrational energy terms, respectively. Resonance interactions between the states (010000) and (000200) were taken into account in the Hamiltonian used to fit upper energies of the (010000) state. The rovibrational energies of the (020000) state were fitted with a Hamiltonian for an isolated vibrational state.