Accurate determination of low state rotational quantum numbers (J < 4) from planar-jet and liquid nitrogen cell absorption spectra of methane near 1.4 micron

0346348 - ÚFCH JH 2011 RIV GB eng J - Journal Article
Votava, Ondřej - Mašát, M. - Pracna, Petr - Kassi, S.
Accurate determination of low state rotational quantum numbers (J < 4) from planar-jet and liquid nitrogen cell absorption spectra of methane near 1.4 micron.
Physical Chemistry Chemical Physics. Roč. 12, č. 13 (2010), s. 3145-3155. ISSN 1463-9076. E-ISSN 1463-9084
R&D Projects: GA AV ČR IAA400400706
Institutional research plan: CEZ:AV0Z40400503
Keywords : spectroscopy * absorption spectra * physical chemistry
Subject RIV: CF - Physical ; Theoretical Chemistry
Impact factor: 3.454, year: 2010

An improved procedure for accurate determination of empirical lower state rotational quantum numbers from molecular absorption spectra is demonstrated for methane. We combine the high resolution absorption spectra in the 7070-7300 cm(-1) frequency range obtained in liquid nitrogen cooled cryogenic cell (T = 81 K) and in supersonic planar jet expansion (T-R = 25 K). Empirical lower state energies of 59 transitions are determined from the ratio of the absolute absorption line strengths at 25 and 81 K. The procedure relies on the realistic description of rotational state populations in the supersonic jet expansion where non-equilibrium nuclear spin isomer distributions are generated due to the rapid cooling. The accuracy of the experimental determination of the lower state energies with J <= 3 is found to considerably improve the results of the same approach applied to spectra at 296 and 81 K.
Permanent Link: http://hdl.handle.net/11104/0187401