R. Anttila

Infrared spectrum of CO2 in the region of the bending fundamental ν2

Abstract The infrared spectrum of CO 2 in the region 540–830 cm −1 has been studied with a Fourier spectrometer at a resolution of 0.010 cm −1 . In addition to the fundamental ν 2 , more than 10 “hot” band transitions of 12 C 16 O 2 have been identified. The rotational constants involved have been derived. Special care has been taken in obtaining accurate constants for the level 01 1 0. The ν 2 fundamentals of the isotopic molecules 13 C 16 O 2 , 16 O 12 C 18 O, and 16 O 12 C 17 O have also been observed in a natural sample.

The infra-red spectrum of C2D2 in the region of the bending fundamental v 5

The absorption spectrum of C2D2 in the region of the bending fundamental v 5 has been studied at a resolution better than 0·03 cm-1. In addition to the fundamental, all the hot bands starting from the levels v 4 and v 5 have been investigated. Several molecular parameters have been derived. Special attention has been paid to illustrate the analysis of the effects of the l-type resonances on the vibrational levels 2v 5 and (v 4 + v 5). The fundamental v 5 of the isotopic molecule 12C 13CD2 has also been observed.

High-resolution infrared spectrum of the v 3 and v 6 bands of HCF3 and of their hot bands

The infrared spectrum of fluoroform has been recorded between 480 and 730 cm-1 at a resolution of 0·03 cm-1. The v 6 perpendicular band at 507·8228 (6) cm-1, heavily perturbed by an l(2,2) type rotational resonance, has been analysed in the P and R as well as in the Q branches. The v 3 parallel band at 700·1009 (6) cm-1 has also yielded molecular constants including C″ - C′. Each of these bands is accompanied by hot bands among which v 3 + v 6 - v 6 and 2v 6 - v 6 deserved special attention since both the upper and lower states of these transitions are perturbed.

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.

The infrared bands ν2 and ν5 of CH3Br with Coriolis interaction

Abstract The infrared bands ν 2 and ν 5 of CH 3 Br have been measured at a resolution of 0.015 cm −1 . The lines due to the isotopic species CH 3 79 Br and CH 3 81 Br were resolved and altogether about 3000 lines were assigned. The bands were analyzed simultaneously by taking into account the xy -Coriolis resonance between the states v 2 = 1 and v 5 = 1. A local perturbation observed in ν 5 could be explained in terms of a (1,−2) resonance between v 2 = 1 and v 5 = 1. Some perturbation allowed transitions could be assigned and they give an equation between A 0 and D 0 K .

Analysis of the ν1 band of CH3I

Abstract The rotational structure of the infrared band ν 1 of CH 3 I has been studied at a resolution of 0.04 cm −1 using a grating spectrometer. In the analysis including 470 lines a resonance, explained to be caused by ν 2 + 2 ν 6 ±2 , has been taken into account. The molecular constants derived include, e.g., α 1 A = 0.051129(14) cm −1 and α 1 B = 0.0983(9) × 10 −3 cm −1 .

The infra-red spectrum of C2HD around 700 cm-1

The absorption spectrum of C2HD in the region of the bending fundamental v 5 has been studied. In addition to the fundamental, all the hot bands starting from the vibrational levels v 4 and v 5 have been investigated. Several molecular parameters have been derived. Special attention has been paid to the effects of l-type resonances on the vibrational levels 2v 5 and v 4 + v 5.

A preliminary determination of the A 0 rotational constant of propyne

The A 0 rotational constant of a symmetric top molecule can be reached by combining data from three infrared bands, νt, (νt+νt′)±2 and νt+νt′−νt where νt and νt′, are two degenerate modes. This method is applied to propyne CH3−C≡CH, with νt=ν10 and νt′=ν8. Unfortunately only one set of K values, corresponding to the difference between K=3 and 0, is available at present. A detailed study of the two K. ΔK=1 subbands present in ν8+ν10−ν10 gives A 0=5·3082 (22)cm−1 but when better spectra of ν10 are analysed, the uncertainty can be decreased by an order of magnitude.

High-resolution study of the infrared band ν8 of CH3CN

Abstract The lowest fundamental band ν8 of CH3CN, around 365 cm−1, has been measured on a Bruker Fourier transform spectrometer at a resolution of 0.0035 cm−1. About 2000 lines have been assigned in 23 subbands. In the analysis the l(2, 2) resonance has been important. The standard deviation 0.16 × 10−3 cm−1 has been reached in the fit with 8 fixed nonzero ground state constants and 16 free parameters. A simultaneous analysis together with pure rotational lines from the literature has also been performed in order to get an even better set of molecular parameters. By combining this work and measurements of the ν7 + ν8 and ν7 + ν8 − ν8 bands it has been possible to determine the ground state constants A0 and D0K. The very preliminary results, 5.27362 cm−1 and 94.2 × 10−6 cm−1, respectively, have been used in the analysis.

The Coriolis interaction between the fundamentals ν2 and ν5 of CD3Br

Abstract The bands ν 2 and ν 5 of CD 3 Br have been measured at a resolution of 0.010 cm −1 . They were analyzed simultaneously by taking into account the xy -Coriolis interaction. More than 1600 transitions were assigned for each isotopic species CD 3 79 Br and CD 3 81 Br. The Coriolis coupling term proved to be ζ 2,5 y = 0.559. The band centers are (in cm −1 ) ν 2 : 991.401 (CD 3 79 Br), 991.390 (CD 3 81 Br); ν 5 : 1055.474 (CD 3 79 Br), 1055.471 (CD 3 81 Br).