HIGH-RESOLUTION SPECTROSCOPY OF (PENTAD DYAD) AND (OCTAD PENTAD) HOT BANDS OF METHANE IN A SUPERSONIC JET

Pulsed jets of heated methane (850 K) have been investigated by high-resolution diode laser spectroscopy in the 8-μm region. The observation of hot band transitions with lower states as high as 3000 cm-1shows that the cooling effect does not modify the distribution of levels between the vibrational polvads. Among the 45 observed lines in the narrow ranges which have been recorded, 18 have been assigned to (pentad-dyad) and 21 to (octad-pentad) transitions. If a common rotational temperature is assumed, a full description of the energy distribution in the hot jet requires the definition of a vibrational temperature for each polyad. A rotational temperature of 200 ± 10 K has been deduced from the analysis of the strengths of the 2ν3Q-branch lines at 1.66 μm. Vibrational temperatures for distributions between polyads and for dyad and pentad cases have been found to be 830 ± 70, 220 ± 25, and 360 ± 80 K, respectively. © 1993 Academic Press, Inc.