Laser Excitation and Equilibration of Excited Vibrational States in CH3F

CH₃F, when its ν₃ mode is pumped by the P(20) line of the 9.6‐μ band of a CO₂ Q‐switch laser, exhibits fluorescence from the ν₁ and ν₄ modes at 3000 cm⁻¹. This fluorescence has a risetime $\text{≤ 5\hspace{0.17em} μ}\sec$ at 1 torr and a decay rate of $\text{0.59± 0.02\hspace{0.17em}}{\mathrm{msec}}^{\text{−1}}·{\mathrm{torr}}^{\text{−1}}$ . The diffusion coefficient measured from the low pressure fluorescence decay curves is $\text{0.076± 0.011\hspace{0.17em}}{\mathrm{cm}}^2·{\mathrm{torr\; msec}}^{\text{−1}}$ . A very efficient near resonant energy transfer process is probably responsible for propagation of energy up the vibrational manifold. Similar processes may be important for laser induced chemical reactions. A square dependence of the intensity of fluorescence on incident cw laser power has been observed. This appears to arise mainly from population changes caused by a general temperature increase in the gas which occurs after absorption of laser energy and equilibration of all degrees of freedom of the molecule.