S. Alanko

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.

Updating OCS 2ν2 band for calibration purposes

Abstract After our previous measurement of the OCS 2 ν 2 band, which was published by Tolonen et al. in J. Mol. Spectrosc. 144 , 18–26 (1990), a clear shift has been found in the OCS ν 1 band, which was our initial calibration source. Because the lines of the 2 ν 2 band are widely used for calibration purposes, we decided to remeasure the band by calibrating it directly with the highly accurate 9.4-μm band of CO 2 . The new center of the OCS 2 ν 2 band is 1047.042051 cm −1 with an accuracy of ±6 × 10 −6 cm −1 . This value is in perfect agreement with the result from the global rovibrational analysis of OCS by Fayt et al. in J. Mol. Spectrosc. 136 , 233–266 (1986). The wavenumber list of the main band is given. The reliability of the calibration accuracy in a high-resolution commercial instrument Bruker IFS 120 HR is examined.

Investigations on the infrared spectrum of acetylene between 2500 cm-1 and 2800 cm-1 and studies of the resonance effects

The Fourier transform infrared spectrum of acetylene between 2500 cm-1 and 2800 cm-1 has been studied at the Doppler limited resolution of 0·0070 cm-1. The combination band v 2 + v 1 5 and the hot bands (v 2 + 2v 5)2,0 ← v 1 5, v 1 ← v 1 5, v 3 ← v 1 4 and (v 2 + v 4 + v 5)2,0 ← v 1 4 have been analysed considering especially the rotational and vibrational l-type resonances. Also the Fermi-type resonance between the υ3 = 1 energy level and the Σ+ u component of the υ2 = υ4 = υ5 = 1 level has been explicitly taken into account. As a result, the vibrational and rotational constants and the resonance parameters for the bands investigated have been obtained.

Overtone bands 2ν3 of 12CH3I and 13CH3I

Abstract The infrared bands 2 ν 3 of 12 CH 3 I and 13 CH 3 I have been investigated at a resolution of about 0.003 cm −1 . Both the bands, one at 1059.9934 and the other at 1028.1201 cm −1 , respectively, are very similar and they have a special feature, a bandhead, in the R branch. In both the bands about 1100 lines with J max ≈ 60 and K max = 12 have been assigned. In the analyses the model for an unperturbed parallel band could be used. In the fits the H constants fixed to ground state values have been included. Standard deviations of 0.11 × 10 −3 cm −1 and 0.13 × 10 −3 cm −1 , respectively, have been attained. Molecular constants related to the bands are given. The hot bands 3 ν 3 - ν 3 have also been studied and the results are very similar to these from the corresponding 2 ν 3 bands. The assignments of some optically pumped FIR laser lines are discussed.

Ground state “supercombination differences” as the method of determination of splittings for faintly polar symmetric top molecules: the CHD3 molecule

Abstract A method, called the procedure of supercombination differences, has been developed in order to determine the a1−a2 (K = 3) ground state splittings for symmetric top molecules from infrared spectra. By forming normal combination differences corresponding to both the components and then their differences the splittings were evaluated for the CHD3 molecule up to J = 20 with the aid of 11 rotation-vibration bands. By applying the theoretical J dependence of the splittings they could be well explained with one parameter 2h3 = 2.2960(90) × 10−10 cm−1.

Hot bands in the region of the v 5 band of HCCI: the Fermi resonance v 3 = 1/v 5 = 2

The Fourier transform infrared spectrum of monoiodoacetylene, HCCI, between 180 cm-1 and 320 cm-1 has been studied at a resolution of 0·0010 cm-1. The hot bands, v 3 ← v 1 5, 2v 0 5 ← v 1 5 and 2v 2 5 ← v 1 5, associated with the v 5 fundamental have been analysed by considering especially the Fermi resonance between the levels v 3 = 1 and v 5 = 2. The next layer of the hot bands, (v 3 + v 5)1 ← v 3, (v 3 + v 5)1 ← 2v 0, 2 5, and 3v 1, 3 5 ← 2v 0, 2 5, has been analysed by taking into account the Fermi resonance between the levels v 3 = v 5 = 1 and v 5 = 3. Also the various l responances at the overtone levels have been considered. As a result, the vibrational and rotational constants and the resonance parameters for the vibrational levels investigated have been obtained.

Ground-state constants A 0 and DK 0 of 12CH3I from perturbation-allowed transitions

The upper levels of the bands v 5 and v 3 + v 6 of CH3I are coupled through a Fermi and an l(2, -1) resonance. This gives rise to perturbation-allowed transitions. Altogether, more than 200 such lines corresponding to three different K-value pairs have been observed between 1320 cm-1 and 1520 cm-1. By fixing the sextic constant HK 0 equal to zero, the following values were obtained: A 0 = 5·173931(2) cm-1 and DK 0 = 87·36(6) × 10-6 cm-1. The possible values of HK 0 and their effects on the results are discussed.

High resolution fourier transform infrared spectroscopy on CH 2 DI and CHD 2 I: evaluation of the ground state constants and analyses of the C-I stretching bands ¿ 3

The high resolution (0.0010cm - 1 ) Fourier transform infrared spectra of the partially deuterated methyl iodide molecules CH 2 DI and CHD 2 I have been recorded and analysed in the v 3 band regions around 510cm - 1 . The fundamental band v 3 is associated with the stretching of the C-I bond and the spectra appear therefore as an asymmetric rotor hybrid a/b-type band and hybrid a/c-type band for CH 2 DI and CHD 2 I, respectively. About 4700 transitions in the case of CH 2 DI and about 3900 transitions in the case of CHD 2 I have been assigned. The ground state rotational constants of CH 2 DI and CHD 2 I have been obtained using the ground state combination differences calculated from the assigned v 3 transitions and 16 microwave transitions from literature. The S reduced Watsons Hamiltonian has been used in the calculations. In addition, the upper state parameters describing the v 3 = 1 vibrational states of these molecules have been determined. The obtained ground state constants as well as the upper state parameters have been compared to the corresponding constants of the symmetric top species CH 3 I and CD 3 I.

The ν3 band of CH3I around 533 cm−1

Abstract The region of the lowest fundamental band ν 3 of CD 3 I around 500 cm −1 is studied at a resolution of 0.015 cm −1 . The K structure in the parallel band ν 3 is resolved for K = 6 – 14. Molecular constants for the ν 3 level are derived, including α 3 A = 3.055(13) × 10 −3 cm −1 . The “hot” band 2 ν 3 - ν 3 is also investigated.

Ground-state constants A 0, D K 0 and H K 0 of 12CH3I from normally allowed infrared absorption bands

The fundamental band v 6, its hot band 2v 6-v 6 and the overtone band 2v 6 of 12CH3I were assigned. Using the lines of these three bands, ground state combination differences that differ in K by three were calculated for eight K value pairs from (3,0) to (10,7). The ground state constants A 0, D K 0 and H K 0 of 12CH3I were then determined and the results are A 0 = 5·173 9358(10)cm-1, D K 0 = 87·63(3) 10-6cm-1 and H K 0 = 4·53(22)10-9cm-1. The constant H K 0 was determined for the first time.