Knowledge Bank

A He-Ne gas laser $(2950cm-1)$ has been used to excite the asymmetric stretch $(\nu a)$ of methane. Vibrational fluorescence has been observed from the $\nu 4$ mode around $1300cm-1$. Detailed study of the phase lag between excitation and fluorescence has allowed us to determine not only the relaxation time of the $\nu 4$ mode $(pr=1.7\mu \sec .atm)$ but also the time for relaxation of vibrational energy from $\nu 4$ to $\nu 4(pr=6\pm 2nsec.atm)$. We believe this to be the first direct measurement of a vibration-vibration relaxation time in a polyatomic molecule. This work supported from grants from the National Science Foundation and from ARPA.