Nonequilibrated energy distribution in polyatomic molecules: The infrared MPD of cyclobutanone

Phillip John, Mark R. Humphries, Robert G. Harrison, Philip G. Harper

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3 Citations (Scopus)


The TEA CO2 infrared MPD of cyclobutanone, on irradiation of the ?24 fundamental mode, has been investigated as a function of incident fluence Fi, wavelength and pressure. Dissociation proceeds via two molecular routes; the first yields ethylene plus ketene CH 2CO, and the second cyclopropane and CO plus minor amounts of propylene. The branching ratio R=[C2H4]/[C 3H6] increases dramatically at pressures less than ~3 Torr from the high pressure thermal limit. This nonthermal feature is most pronounced at low Fi. The average number of quanta absorbed per molecule , measured by pyroelectric and optoacoustic detection, is independent of cyclobutanone pressure between 0.1 and 10.0 Torr. varies linearly with Fi in the range investigated 0.2-2.0 J cm -2. An explicit formulation of the infrared MPD process is presented based on a truncated s-fold degenerate harmonic oscillator approach. Vibrational energy transfer is incorporated via v-v bimolecular collisions. The predicted dependence of R on pressure is in good agreement with the experimental data presented herein. Moreover, the observed linear dependence of with Fi, and its independence with respect of pressure, is also borne out by this theory. © 1983 American Institute of Physics.

Original languageEnglish
Pages (from-to)1353-1359
Number of pages7
JournalThe Journal of Chemical Physics
Issue number3
Publication statusPublished - 1983


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