Partial vibration energy transfer map for methyl fluoride: A laser fluorescence study

Infrared fluorescence has been observed from the 2ν₃ overtone, the ${\nu }_3{\mathrm{+\nu }}_6$ combination band and the ν₁, ν₂, ν₄, ν₅, and ν₆ fundamentals of CH₃F after pumping of the ν₃, $\text{0→ 1}$ 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 $\text{0.59\hspace{0.17em}}{\mathrm{msec}}^{\text{−1}}·{\mathrm{torr}}^{\text{−1}}$ . The fluorescence risetimes of the ν₆, ν₂ and ν₅, ν₁ and ν₄, and 2ν₃ states were also observed. The rate of rise of the ν₁ and ν₄ fluorescence and the 2ν₃ fluorescence is faster than 7 μsec at 1 torr. The ν₆ fluorescence risetime is pressure dependent with a rate constant of $\text{106± 21\hspace{0.17em}}{\mathrm{msec}}^{\text{−1}}·{\mathrm{torr}}^{\text{−1}}$ . The pressure dependent rate of rise of the ν₂ and ν₅ fluorescence is $\text{86± 17\hspace{0.17em}}{\mathrm{msec}}^{\text{−1}}·{\mathrm{torr}}^{\text{−1}}$ . 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.