Extended assignments of the 3ν1+ν3 band of methane

Abstract

The 3ν1+ν3 band of methane has been investigated using a titanium sapphire laser (TSL) spectrometer. This band has recently been studied by others, and 31 transitions were assigned [Boraas et al., J. Chem. Phys. 100, 7916 (1994)]. In this work, the tone-burst modulation spectrum at liquid nitrogen (77 K) and room temperature (295 K) has been recorded to determine the rotational quantum number J″ of the lower level of each transition. Stark modulation spectra were also recorded at room temperature by applying a 40 kV/cm electric field to identify the E symmetry and other species. Among the 269 transitions observed in the 77 K tone-burst modulation spectrum, we have assigned 215 transitions with respect to J″, of which 49 are identified up to their tetrahedral components. We found a congested band structure that results from the large fraction of dark vibrational states that derive their intensity from a single bright state as a result of Coriolis interactions.

Empirical low energy values for methane transitions in the 5852–6181cm−1 region by absorption spectroscopy at 81K

“…[4] used two spectra recorded at 295 and 149 K by Fourier Transform Spectroscopy (FTS) to determine lower state quantum numbers in the region of the 3m 3 band near 9000 cm À1 , Tsukamoto et al [5] could assign 215 transitions with respect to J 00 among the 269 transitions of the 3m 1 + m 3 that they recorded at 77 K. Of particular relevance for this study is the investigation by Margolis of the 5500-6150 cm À1 spectral region by FTS at room [6] and reduced [7] temperatures. Using spectra recorded at 180-220 K with a 0.8 m long cryogenic cell, he could derive the lower energy value, E 00 of 1600 transitions.…”

The near-infrared (1.30–1.70 μm) absorption spectrum of methane down to 77 K

“…On the other hand, direct sample cooling is the simplest experimental way to reduce the spectral congestion and simplify the rovibrational analysis. Absorption spectra of methane cooled down to 77 K using cooled cells could already be investigated in several spectral regions, [5][6][7][8][9][10][11][12] thanks to the important available vapor pressure (B10 Torr). Further cooling was also achieved by means of supersonic expansions.…”

“…7). Among the experimental investigations of the absorption spectrum of CH 4 in a cell cooled at low temperature [5][6][7][8][9][10][11][12], two studies used this method: Pierre et al [8] show that the measurement from Doppler line broadening is a very precise way to measure the gas temperature in a cooled cell.…”

“…Absorption spectra of methane cooled down to 77 K using cooled cells could already be investigated in several spectral regions [5][6][7][8][9][10][11][12], thanks to the important available vapor pressure (~10 Torr). Further cooling was also achieved by means of supersonic expansions [11,[13][14][15][16][17][18][19].…”

Detection of vibrational overtone excitation in methane by laser‐induced grating spectroscopy

“…1 More recently, a variety of methods has been developed and applied for extended investigations of methane transitions. Intracavity laser absorption (ILA), 3 intracavity photoacoustic 4,5 and tone-burst modulation 6 spectroscopy have been used to characterize methane bands around 11 300 cm 1 . In addition, the high sensitivity of the intracavity laser technique has been utilized to measure the absorption spectra and coefficients between 10 635 and 13 300 cm 1 by O'Brien and Cao.…”