Infrared fluorescence has been observed from the 2ν3 overtone, the ν3+ν6 combination band and the ν1, ν2, ν4, ν5, and ν6 fundamentals of CH3F after pumping of the ν3, 0→1 transition by the P (20), 9.6 μ line of a Q-switched CO2 laser. All observed states exhibit a single exponential decay curve with a rate of 0.59 msec-1.torr-1. The fluorescence risetimes of the ν6, ν2 and ν5, ν1 and ν4, and 2ν3 states were also observed. The rate of rise of the v1 and ν3 fluorescence and the 2r3 fluorescence is faster than 7 μsec at 1 torr. The ν6 fluorescence risetime is pressure dependent with a rate constant of 106±21 msec-1 · torr-1. The pressure dependent rate of rise of the ν2 and ν5 fluorescence is 86±17 msec-1 ·torr-1. Measurements of the steady state dependence of the ν2 and ν5 fluorescence intensity versus laser intensity were made. The temperature dependence of the Q-switch excited fluorescence intensity from the 2ν3 and ν1 and ν4 states was also studied. No evidence of excited state absorption was observed and both sets of measurements indicate collisional processes rather than excited state absorption play the major role in establishing an equilibrium among the excited vibrational states of CH3F. The ramifications of these results for energy transfer mechanisms, laser action, and laser induced chemical reactions in polyatomic molecules are discussed.
ASJC Scopus subject areas
- Physics and Astronomy(all)
- Physical and Theoretical Chemistry