Claude Alamichel

Rotational analysis of the ν2 + ν6±1, ν5⊣1 + ν6⊣1, ν5⊣1 + ν6±1, and 2ν3 + ν6±1 interacting infrared bands of methyl chloride

Abstract The rotational analysis of the infrared absorption of CH 3 35 Cl and CH 3 37 Cl between 2280 and 2580 cm −1 has been carried out on a Fourier transform spectrum with a resolution of 0.005 cm −1 . The bands ν 2 + ν 6 ( E ), ν 5 + ν 6 ( E + A 1 + A 2 ), and 2 ν 3 + ν 6 ( E ) occurs in this region, giving rise to several widespread and local perturbations. The l -type doubling effects observed in the ν 5 + ν 6 vibrational system involve the mixing of perpendicular and parallel components, and are analyzed in detail. Substantial improvements in the analysis are achieved with respect to previous works (C. Alamichel and C. di Lauro, Mol. Phys. 30 , 73–79 (1979); C. di Lauro, G. Guelachvili, and C. Alamichel, J. Phys. 37 , 355–358 (1976)) and a value of the A ″ rotational constant is given from the analysis of perturbation-allowed transitions.

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.

Study of the v1 infrared band of ONCl

498 A-type rotational lines of the v1 band of 16O14N35Cl around 1800 cm−1have been assigned; a least-squares calculation over them, with a rms deviation of 0.0015 cm−1, has made it possible to measure several constants of the (100) vibrational level.

Study of the spectrum of CH379Br between 1520 and 1700 cm−1: The ν3 + ν6 and the ν5 rovibrational bands

Abstract The ν 3 + ν 6 band of CH 3 79 Br has been directly analyzed for the first time, and an r.m.s. standard deviation of 0.0035 cm −1 was obtained over 394 lines of K ″Δ K = 2 up to 12, through a least-squares calculation using an unperturbed model. Nevertheless discrepancies occur on sub-bands with K ″ ⩾ 9, which remain not yet understood. In particular it seems difficult to explain them by a Fermi resonance with the ν 5 band, since it has been possible to fit properly around 580 lines of this band, belonging to sub-bands K ″Δ K = 7 up to 16, taking only into account the Coriolis resonance with the ν 2 band and the l (2,2) resonance of ν 5 .

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.

Fourier transform high resolution study of the 3v 2, 2v 2+v 5, v 2+2v 5/0 and 3v 5/±1 rovibrational bands of CH3 79Br from 3830 cm−1 to 4300 cm−1

About 2000 lines of the four bands quoted in the title have been assigned. A root-mean-square deviation of about 0·0235 cm−1 has been achieved by a least-squares fit over 1771 lines. For this purpose, a model involving 15 levels, linked either by the x-y Coriolis resonance between the v 2 and v 5 modes or by slight anharmonic resonances, was used. Several perturbations remain unexplained in the 3v 5/±1 band, the centre of which is shifted by the Fermi resonance between the v 5=3±1 and the (v 1=1,v 5 ±1), levels.

The perpendicular v ∓1 4 + v ∓1 6 component of the rovibrational v 4 + v 6 band of CH3 79Br, studied in a high resolution FTIR spectrum from 3870 cm-1 to 4110 cm-1

860 rotational ines of the almost unperturbed v ∓1 4 + v ∓1 6 component of the v 4 + v 6 band of CH3 79Br have been assigned in spite of overlaps with several other bands. Only a few sub-bands (KΔK = 1, -7, -8, -9) are subject to slight resonances. An RMS deviation of 0·0039 cm-1 has been achieved by a leastsquares fit of 742 lines. As expected, the A′, B′, D′J , D′JK and D′K molecular conparison between the centres of both components of the v 4 + v 6 band allowed us to measure two anharmonicity constants: x 46 = -5·25 cm-1 and g 46 = 0·89 cm-1.

Study of overtones and combination bands in the infrared spectrum of ONCl

Abstract The 2ν 1 , 2ν 1 +ν 3 , 2ν 1 +ν 2 , 2ν 1 +2ν 2 , 3ν 1 , 3ν 1 +ν 3 and 4ν 1 infrared bands of ONCl have been recorded. A least-squares calculation over a few lines of the 3ν 1 band of 16 O 14 N 35 Cl, with arms deviation of 0.003 cm − , provided values for several constants of the ν 1 =3 level.

Anharmonic resonances between the upper rovibrational levels of the and infrared bands of CH3 35Cl studied in a high-resolution FTIR spectrum from 4250 to 4600 cm-1

82 K ΔK sub-bands, belonging to the eight vibrational bands of monoisotopic CH3 35Cl that are quoted in the title, have been identified. An r.m.s. standard deviation of 0·051 cm-1 has been achieved by a least-squares fit of 79 Q-branch head wavenumbers. For this purpose, a simplified model, taking into account anharmonic resonances between was used. For two of the three sub-bands not considered in the calculation, the difference between observed and calculated wavenumbers is small (0·2 cm-1); for the last one, it is much larger (1·18 cm-1), and this is probably caused by the upper level of , which has not been taken into account in the present model, because of the lack of information related to this band.

Rovibrational analysis of weaker bands (ν3 + ν4 + ν6, ν2 + ν3 + ν4 − ν3, ν3 + ν4 + ν5 − ν3 and ν1 + ν5) of CH379Br in the range of 2.5 μm

Abstract All the bands of the CH 3 79 Br isotopomer quoted in the title have been studied in high resolution (0.006 cm −1 ). A least squares fit over 580 lines (194 being zero-weighted) of ν 3 + ν 4 + ν 6 E, according to an unperturbed model, gave a r.m.s. deviation of 0.005 cm −1 with quite reasonable molecular constants. A least squares fit over 824 lines (171 being zero-weighted) of both ν 2 + ν 3 + ν 4 − ν 3 and ν 3 + ν 4 + ν 5 − ν 3 hot bands, linked by the x − y Coriolis resonance which connects the ν 2 and ν 5 modes [C. di Lauro and I.M. Mills, J. Mol. Spectrosc., 21 (1966) 386], was achieved according to a model taking also into account the l (2,2) resonance [M.-L. Grenier-Besson, J. Phys. (Paris), 21 (1960) 555, and G.J. Cartwright and I.M. Mills, J. Mol. Spectrosc., 34 (1970) 415] inside the ν 4 mode; it gave a r.m.s. deviation of 0.027 cm −1 . The ν 2 + ν 3 + ν 4 − ν 3 band overlaps the ν 1 + ν 5 band on its Δ K = −1 side, making quite difficult the assignments of this latter band, 1020 lines of which have nevertheless been identified. Moreover ν 1 + ν 5 is strongly perturbed by both perpendicular components of the ν 3 + 2ν 5 + ν 6 band, which are too weak to be normally observed and are only reached because of their interactions with ν 1 + ν 5 .