Mireille Morillon-Chapey

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 ) .

High‐resolution absorption cross sections of chlorine nitrate in the ν2 band region around 1292 cm−1 at stratospheric temperatures

The infrared absorption spectrum of ClONO2 has been recorded between 500 and 1600 cm−1 at temperatures between 188 K and 222 K and resolutions of up to 0.004 cm−1. The infrared absorption cross sections were determined for the entire ν2 band between 1260 and 1320 cm−1. The cross sections (with 0.025 cm−1 resolution) for the central Q branch absorption maximum at 1292.68 cm−1 are (in 10−18 cm2 molecule−1) 3.12±0.06 at 201 K, 3.45±0.15 at 211 K, and 3.31±0.06 at 222 K. The influence of resolution on the cross section of the Q branch maximum is small only for resolutions between 0.025 and 0.100 cm−1. In the P and R branches, the cross sections change considerably with increasing resolution. The new absorption cross sections are important for the determination of stratospheric ClONO2 concentrations from atmospheric infrared absorption spectra and for modeling atmospheric transmission in the spectral region around 1292 cm−1.

The 923-cm−1 band of CF235Cl2 (freon 12), studied by infrared-microwave double resonance

Abstract The constants of the 923-cm −1 band ( ν 6 ) of CF 2 35 Cl 2 were accurately determined by the application of infrared-microwave double resonance using CO 2 and N 2 O lasers. The frequencies of 32 ground-state and 34 ( v 6 = 1) state rotational transitions and 14 infrared transitions were measured. The infrared transition frequencies were generally obtained with an accuracy of ± 20 MHz, but in some cases observation of two-photon Lamb-dips allowed the accuracy to be improved to ± 5 MHz. Many double-resonance signals displayed a predominantly “dispersion-type” lineshape and it has been shown that the phase of the observed signals gives information over the relative disposition of the energy levels involved.

Intensities of the v1-bands of 12CH335Cl and 12CH337Cl near 3 μm

Abstract Strengths of individual lines in the v1 fundamental of methyl chloride have been measured at low pressure and at 296.35 K using a Fourier transform interferometer. The band strengths Sv0 obtained by fitting these measurements are 85.8±1.0 and 86.6±1.0 cm-2 atm-1 for 12CH335Cl and 12CH337Cl, respectively. The Q3-branch appears to be useful for atmospheric detection of methyl chloride.

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.

The ν6 band of CF235Cl37Cl from IR−MW double resonance

Abstract Effective constants for the ν 6 band of CF 2 35 Cl 37 Cl have been determined from the analysis of infrared-microwave double-resonance data.

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.

Infrared spectra of CH3Br: The 2ν2 band near 2600 cm−1

Abstract The rotational fine structure of 2 ν 2 has been studied under high resolution (0.03 cm −1 ) for CH 3 79 Br and CH 3 81 Br. About 700 lines have been assigned for each isotopic species. The band centers have been found at 2596.871 and 2596.815 cm −1 , respectively.