Rovibrational Analysis of Symmetric Top Molecules: ν7 Band of CH3CCD

Abstract

The high-resolution infrared absorption study of polyatomic molecules is of great interest. Availability of intense sources in infrared region and with the progress made in theoretical techniques, it is possible to do line by line analysis of polyatomic spectrum. Many a times, the analysis of high-resolution spectra requires the inclusion of various vibration–rotation interactions. Sometimes the interacting state could be a state to which transitions are not observed in the spectrum called as “shadow” state. In this article, we present the results of the analysis of ΔJ = 0, ±1; ΔK = ±1 sub-bands with Kmax = 3 and Jmax = 45 of the high-resolution spectrum of ν7 band of CH3CCD molecule for the first time. The room temperature Fourier transform infrared (FTIR) spectrum of CH3CCD in the region 1300–1600 cm−1 was recorded at an apodized resolution of 0.004 cm−1 which covers the ν7 fundamental band of CH3CCD. Approximately 1500 rotational lines consisting of total of 12 sub-bands of ν7 band of CH3CCD have been assigned. The rovibrational analysis has been carried out by taking into account the strong x–y Coriolis interaction of the ν7 = 1 state with the ν4 = 1 “shadow” state. The band center and the rotational constants, B and (A–B) of ν4 = 1 state were also derived accurately from the perturbation analysis in this work.