Michel Betrencourt

Infrared emission spectrum of the radical 28SiH: Observation and analysis of the rovibrational bands 1–0, 2–1, and 3–2 in the X 2Π ground state

The emission spectrum of a plasma of silane flowing through a multipass reactor and excited by a radio frequency discharge has been recorded with a high information Fourier transform spectrometer. 192 rovibrational transitions of the 28SiH radical, between 1800 and 2150 cm−1, have been measured in the electronic ground state. These transitions are related to the fundamental band 1–0 and the two hot bands 2–1 and 3–2. A least squares procedure have led to the determination of a unique set of 25 accurate molecular constants for the vibrational levels v=0, 1, 2, 3 of the X 2Π state. The standard deviation on the calculated frequencies is 7×10−4 cm−1.

Diode laser spectroscopy of methyl chloride near 14 μm toward its detection in the stratosphere

Abstract Detection of CH 3 Cl in the Earths atmosphere by infrared techniques is a subject of current interest. The ν 3 band, centered at 732 cm −1 , has lines as strong as those of ν 1 , centered at 2970 cm −1 , and we show that they can be useful for a high-resolution detection. A complete study of the absorption spectrum of this molecule in the region 660–770 cm −1 has been performed. On spectra recorded using a tunable diode laser spectrometer, with the spectral resolution limited by the Doppler width (0.0014 cm −1 ), we have assigned the ν 3 band lines related to four isotopic species: 12 CH 3 35 Cl, 12 CH 3 37 Cl, 13 CH 3 35 Cl, and 13 CH 3 37 Cl. In addition, the hot band 2 ν 3 - ν 3 for 12 CH 3 35 Cl has been observed. The calculated molecular constants reproduce, for each band, the observed wavenumbers with a rms deviation of 6 × 10 −4 cm −1 . The ν 3 band centers have been found to be 732.8421 and 727.0295 cm −1 for the two main isotopic species, 12 CH 3 35 Cl and 12 CH 3 37 Cl, respectively. The feasibility of detection of methyl chloride in the stratosphere is discussed.

Perturbations study of the high-resolution spectrum of methyl bromide in the range of the fundamental band

Abstract The Fourier transform absorption spectrum of CH 3 Br has been analyzed between 2930 and 3010 cm −1 with a recorded resolution of 0.007 cm −1 . More than 1300 lines have been assigned for each isotopic species. Two bands have been identified: the fundamental parallel band ν 1 and the parallel component of ν 3 + ν 5 + ν 6 . An anharmonic resonance couples the corresponding levels and affects all the K subbands of these bands. Taking account of this resonance and of a vibrational l -type resonance in ν 3 + ν 5 + ν 6 , molecular parameters of these two bands have been determined for the first time. The band centers are (in cm −1 ) v 1 : 2973.184 ( CH 3 79 Br ), 2973.183 ( CH 3 81 Br ) ; v 3 + v 5 + v 8 : 2996.0.094 ( CH 3 79 Br ), 2994.864 ( CH 3 81 Br ) .

Analysis of the high resolution spectrum of the fundamental bandsv2 andv5 of12CH3F and their interactions

Thev2(A1) andv5(E) fundamental vibration-rotation bands of12CH3F have been recorded under high resolution (0.015 to 0.020 cm−1) in the spectral range of 1460 cm−1. About 1100 transitions have been assigned. The Coriolis interaction between v2=1 and v5=1, and the l(2,-1) interaction in v5=1 have been rigorously treated. Sixteen molecular constants have been determined from a least squares analysis. They reproduce the observed data with an overall standard deviation of 0.0037 cm−1.

Rotation-vibration spectrum of CH3F in the range 2000–2100 cm−1

Abstract The spectrum of CH 3 F between 2000 and 2100 cm −1 has been investigated under high resolution (0.025 cm −1 ). Three parallel bands have been analyzed: 2 ν 3 of 12 CH 3 F for which the rotational K structure has been studied, 3 ν 3 - ν 3 of 12 CH 3 F, and 2 ν 3 of 13 CH 3 F. The band center of the main band 2 ν 3 of 12 CH 3 F has been found at 2081.383 cm −1 .

Infra-red spectrum of CH3F at very high resolution : Accidental and essential resonances in ν2 + ν3 and ν3 + ν5 bands

The analysis of the Fourier transform spectrum, with a resolution of 0·008 cm-1, of the combination bands ν2 + ν3 (A1 species) and ν3 + ν5 (E species) of CH3F has allowed the study of x-y Coriolis resonance between the states υ2 = 1 and υ5 = 1. The vibrational levels υ2 = υ3 = 1 and υ3 = υ5 = 1 are 15 cm-1 apart and the interaction is very strong. The combination of the Coriolis resonance and the essential interaction of l-type (2, 2) in ν3 + ν5 gives rise to a ‘giant’ l-type doubling : for J=25 the shift between the levels is about 17 cm-1. A second essential interaction exists in the perpendicular band: the rotational l-type (2, -1) resonance. The effect of this is small, but the addition of this interaction causes a chain of resonances between ro-vibrational levels and gives rise to a doubling of PP3(J) transitions in the perpendicular band. Molecular parameters and coupling constants have been derived.

Etude de la bande 2v4 perpendiculaire du fluorure de methyle vers 6000 cm−1

Abstract The 2 v 4 perpendicular band of methyl fluoride has been investigated under high resolution. The R R k (J) lines have been assigned and measured up to (ItK) = 13, and confirmed by the partly visible fine structure of the r Q branches. The (B′—B″) eff coefficient has been shown to have a strong dependence upon k . The low frequency part of the spectrum is badly perturbed and then the assignment of p P k (J) lines cannot be sure. The assumption of a Coriolis interaction about X-Y axes involving 2 v 4 and 2 v 1 and v 1 + v 4 has been discussed.

Analysis of the interactions between ν2 and ν5 in the vibrational state υ3 = 1 of 12CH3F

Abstract The Coriolis interaction between ν 2 + ν 3 and ν 3 + ν 5 of 12 CH 3 F and the essential l (2,- 1) rotational resonance in ν 3 + ν 5 , have been treated rigorously up to the fourth order of the Hamiltonian. Eighteen spectroscopic constants are necessary to reproduce 820 experimental data with a standard deviation of 0.0013 cm −1 . Parameters of the anharmonic force field have been derived.