Najate Bensari-Zizi

Study of the ν2 + ν3 and 2ν6 infrared bands of CH379Br and CH381Br

Abstract The rotational analysis of the ν 2 + ν 3 band, centered around 1912 cm −1 , and of both components 2 ν 6 ±2 and 2 ν 6 0 , centered about 1912 and 1904 cm −1 , respectively, has been carried out from a Fourier transform spectrum having a resolution limit of 0.005 cm −1 . A standard deviation of about 0.001 cm −1 was obtained for about 750 lines of the unperturbed 2 ν 6 ±2 component for both isotopic species. The ν 2 + ν 3 band, stronger than 2 ν 6 ±2 , is perturbed by two resonances: a Coriolis resonance with the very weak ν 3 + ν 5 band, no line of which has been observed, and an anharmonic resonance with 2 ν 6 0 , only four K subbands of which have been observed. For both isotopic species, a standard deviation of about 0.002 cm −1 has been obtained for about 750 lines of ν 2 + ν 3 and 2 ν 6 0 .

High-resolution FTIR study of the ν1+ν3 and 2ν3+ν5+ν6 rovibrational bands of methyl bromide

Abstract About 1000 lines of both bands ν1 + ν3 and 2ν3 + ν5 + ν6, centered around 3590 cm−1, have been assigned in the case of methyl bromide. An anharmonic resonance has been found between ν1 + ν3 and the parallel component of 2ν3 + ν5 + ν6 with a coupling constant WF = 4.95 cm−1. A rms deviation of 0.0047 cm−1 has been obtained through a least-squares calculation with a simplified model taking into account only the above-mentioned anharmonic resonance and the l vibrational resonance of the 2ν3 + ν5±1 + ν6∓1 parallel component (with the coupling constant R = −3.7 cm−1). Very likely all these parameters are only effective constants because of Fermi resonances not yet completely understood.

Rovibrational analysis of the ν3 + 2ν05, ν6 + 2ν05, 2ν2 + ν5 and ν2 + 2ν05 infrared bands of CH335Cl

In order to study the Fermi resonance between ν1 and 2ν05, the spectrum of the ν3 + 2ν05, ν6 + 2ν05, 2ν2 + ν5 and ν2 + 2ν05 bands has been recorded with a resolution of 0.0075 cm−1; the main features of these four bands have been qualitatively explained and 1450 lines have been assigned; the band centres have been respectively found at 3607.69, 3886.05, 4138.29 and 4230.32 cm−1.

Study of the spectrum of CH335C1 between 4250 and 4600 CM−1: thev2+v4 andv4+v5 rovibrational bands

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.