Study of the spectrum of CH3 35C1 between 4250 and 4600 CM?1: thev 2+v 4 andv 4+v 5 rovibrational bands

Abstract

About 2500 lines of CH335Cl have been assigned. The strong xy Coriolis resonance between thev2 andv5 modes is quite visible between thev4+v4±1 perpendicular band, centered around 4383 cm−1, and thev4±1+v5±1 perpendicular component, centered around 4475 cm−1, with a crossing of upper energy levels allowing the observation of lines which are normally forbidden. Although not yet observed with certainty, because of the great density of lines of the spectrum, thev4∓1+v5±1 parallel component is nevertheless detectable by its effects onv2+v4±1 which is linked by Coriolis resonance to both components ofv4+v5. Moreover the spectrum is much complicated by many other resonances with weak bands which occur at level crossings: it is the case ofv2+3v6±1, connected tov2+v4±1 by the well known Darling Dennison resonance which couplesv4±1 and 3v6±1, and also ofv5±1+3v6±1 connected tov4±1+v5±1 by the same resonance; but this last case is complicated by an anharmonic resonance betweenv5±1+3v6±1 and 2v3+3v6∓1. Two more perturbations occur on the ΔK=−1 side ofv2+v4: a weak Coriolis resonance gives rise to one subband ofv1+v2 at a level crossing withv2+v4, and thev1+v5 band (linked of course tov1+v2 by the Coriolis resonance between thev2 andv5 modes) is quite visible and perturbs several subbands ofv2+v4 of high values of K through an anharmonic resonance. Moreover, the complex (3v5±1,v+2v50, 2v2+v5±1, 3v2,v2+2v5±2, 3v5±3) system of Coriolis-connected bands is linked to the bands studied in the present work by two Fermi resonances: one betweenv2+2v50 andv1+v2, and the other one betweenv1+v5 and 3v5±1, whose several subbands have been observed on the low part of the spectrum. The values of all the band centres and of the different coupling constants have been estimated, but all these interactions make the line assignments and the interpretation of the spectrum very difficult.