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Direct observation of the symmetric stretching modes of (A)over-tilde(1) A(u) acetylene by pulsed supersonic jet laser induced fluorescence

TitleDirect observation of the symmetric stretching modes of (A)over-tilde(1) A(u) acetylene by pulsed supersonic jet laser induced fluorescence
Publication TypeJournal Article
Year of Publication2008
AuthorsSteeves, AH, Merer, AJ, Bechtel, HA, Beck, AR, Field, RW
JournalMolecular Physics
Volume106
Pagination1867-1877
Type of ArticleArticle
ISBN Number0026-8976
KeywordsAB-INITIO MO, acetylene, ASSIGNMENT, C2H2, DEPERTURBATION, excited states, PARTIAL, PHOTODISSOCIATION, S-1((1)A(U)) STATE, SPECTROSCOPY, vibration-rotation analysis, VIBRATION-ROTATION CONSTANTS, vibrational spectroscopy, WAVELENGTH BANDS, X BAND SYSTEM
Abstract

Rotational analyses are reported for the 2(0)(2) and 1(0)(1) bands of the (A) over tilde (1) A(u) <- (X) over tilde (1) Sigma(+)(g) transition of C2H2 near 45,000 cm(-1) (+2800 cm(-1) relative to T-0) from jet-cooled laser-induced fluorescence spectra. While the 220 band is unperturbed and straightforward to assign, the 1(1) level is strongly perturbed by interactions with the 2(1) B-2 polyad, where upsilon B’ = upsilon(4)’ + upsilon(6)’. In order to assign the lines of this band, a population-labelling technique was used, employing an infrared laser to deplete the population in selected ground state rotational levels before probing with the ultraviolet laser. Deperturbation of the 1(1)/2(1) B-2 interaction leads to the value v(1)’ = 2880.08 cm(-1) for the fundamental symmetric C-H stretching frequency. Assignments are also reported for the 2 3 and 1 1 2 1 levels, completing all assignments of levels containing excitation in only the totally symmetric vibrational modes up to + 4500 cm(-1). The reassignment of upsilon(1)’ implies that some of currently accepted assignments above 47,000 cm(-1) are in error and suggests that the interpretation of some aspects of the near-threshold photodissociation measurements of Mordaunt et al. [J. Chem. Phys. 108, 519 (1998)] may need to be revisited.

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