M. Koivusaari

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.

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.

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.

Infrared bands ν8 and 2ν8 of CD3CN

Abstract The high resolution (linewidth 0.0030 cm −1 ) spectrum of the lowest fundamental band ν 8 of CD 3 CN around 334 cm −1 has been measured on a Bruker Fourier transform spectrometer. In the analysis of more than 2000 assigned lines from 32 subbands even the parameters η JJ , η JK , and η KK proved to be significant. A simultaneous fit together with pure rotational lines from literature was also performed. The parallel overtone band 2 ν 8 0 around 661 cm −1 has been measured (linewidth 0.0025 cm −1 ) and analyzed, too. In the analysis of about 1000 lines the l -resonance was essential. The perpendicular 2 ν 8 band was not observed, but using some perturbation allowed lines, hot band 2 ν 8 ±2 - ν 8 ±1 lines, and literature microwave data, the constants for the l = ±2 component of the vibrational state v 8 = 2 were evaluated, too. Among the results the anomalous A ″- A ′ values, 0.77116(30) × 10 −3 cm −1 for the 2 ν 8 0 band and 1.3193(28) × 10 −3 cm −1 for 2 ν 8 ±2 , are striking.

Ground state constants and K-type doubling for allene

Abstract The ground state rotational and centrifugal distortion constants of allene have been determined from a simultaneous analysis of GSCDs obtained from three infrared bands [F. Hegelund, R. Anttila, and S. Alanko, J. Mol. Spectrosc. 141 , 309–316 (1990)] and GSCDs obtained from the perpendicular bands ν 9 and ν 10 . The effect of K -type doubling in the ground state has been observed in the K Δ K = +2 and −2 subbands of ν 9 and ν 10 , and the splitting constant d 2 has been determined including its sign.

The ν4 and ν7 bands of CD3CN with coriolis interaction and other perturbations

Abstract The high resolution (0.0025 cm −1 ) Fourier transform spectrum of CD 3 CN covering the parallel fundamental band ν 4 (831.44 cm −1 ) and the perpendicular fundamental ν 7 (847.10 cm −1 ) was measured. In these bands 970 and 1380 lines, respectively, were assigned. Because of the proximity of the vibrational levels there are strong effects due to the Coriolis interaction. In addition the l (2,2) resonance in ν 7 , a Δ l = ±1, Δ k = ⊣2 resonance between ν 4 and ν 7 and also the Fermi resonance ν 7 2ν 8 −2 were included in the analysis. Molecular constants for the bands as well as the interaction constants are presented.

High-resolution analysis of the ν3 and ν6 bands of CD3Cl

Abstract This paper describes the analysis of the ν 3 and ν 6 fundamental bands of methyl chloride d 3 using a high-resolution spectrum (resolving power of the apparatus: 0.0015 cm −1 ). These bands are coupled by a weak Coriolis interaction and are then treated simultaneously. Spectroscopic constants are derived for the two isotopic species CD 3 35 Cl and CD 3 37 Cl.