Vibrational spectra of chloroform, freon-11 and selected isotopomers in the terahertz region

Abstract

The fundamental bands of the CCl 3 asymmetric deformation modes of selected isotopomers of chloroform (CHCl 3 ) and freon-11 (CFCl 3 ) have been measured in a static cell at ambient temperature using a laser-based source of tunable radiation in the terahertz region of the electromagnetic spectrum.The analysis of the rotational contours of the bands enabled the derivation of the fundamental frequencies with an accuracy of better than 3 GHz.Keywords: THz spectroscopy, vibrational spectrum Spectroscopy in the terahertz (THz) region of the electromagnetic spectrum (0.1-10 THz) is challenging because the generation and detection of radiation in this region is difficult. Despite recent progress with radiation sources in the THz region, such as backward-wave oscillators (BWO) We report here a measurement of the absorption spectra of 12 CHCl 3 ,13 CHCl 3 , CDCl 3 and CFCl 3 with natural isotopic abundance of chlorine in the region of the ν 6 fundamental band. This mode is of e symmetry for the C 3v isotopomers but splits into two modes, ν 6 (a ′ ) and ν 9 (a ′′ ), in isotopomers of C s symmetry (we follow the usual convention for numbering the normal modes, see p. 25 of Ref.[20]).The experimental setup was identical to the one described in Ref.[11] and was placed under an N 2 -purged plexiglas cage to reduce water absorption.12 CHCl 3 , 13 CHCl 3 , 12 CDCl 3 and 12 CFCl 3 were supplied by Sigma-Aldrich (≥ 99.5% purity) and used without further purification. A one-meter-long absorption cell with white, ultra-high molecular weight (UHMW) polyethylene windows was filled with 120 mbar ( frequencies of the ν 6 (a ′ ) and ν 9 (a ′′ ) modes calculated ab initio also appear degenerate within the expected precision limit of the method used (see Table 1).

A Survey of Molecules With Large Nuclear Quadruploes and Other Projects

“…Additionally, out of all eighteen of the previously mentioned halosilanes and halomethanes, only a select few were found to be the focus of spectroscopic studies in the terahertz, far infrared, and infrared frequency regimes [70][71][72][73][74][75][76].…”