Vibrational Energy Distribution through Chemical Laser Studies. I. Fluorine Atoms plus Hydrogen or Methane

Abstract

A new method is described for determining the energy distribution among the product vibrational energy levels in an exothermic reaction. By careful control of the rotational temperature in the UF6–H2(D2) and UF6–CH4(CD4) chemical laser systems, one can obtain conditions for which two hydrogen fluoride vibration–rotation transitions initiate simultaneously and with the same gain. From the relationship between relative gain, rotational temperature, and the vibrational populations, an accurate value can be determined for the ratio of the populations Nυ / Nυ−1 of the two states involved in the first transition to reach laser threshold. This ratio equals kυ/kυ−1 after vibrational deactivation has been taken into account. This technique has yielded the following rate-constant ratios:F + H2→limυHFυ† + H, k2 / k1∼5.5 F + D2→limυDFυ† + D, k3 / k2∼1.6. The significant observations are that the rate-constant ratios are all above unity, the hydrogen and methane values are very close to each other, and the DF ratios are much closer to unity than their HF counterparts.