Efficient V-V energy transfer in a multiphoton excited mixture of SF6and CF4

Spectral and temporal measurements of infrared fluorescence (IRF) in SF
6
, CF
4
, and mixtures of SF
6
and CF
4
gases excited by a pulsed CO
2
laser are reported. Using the 944.2 cm
^-1
[
P(20)
] laser line for excitation and measuring the IRF spectra between 700 and 1500 cm
^-1
, a strong red shifted IRF peak of the ν
3
mode in pure SF
6
was found. No IRF was observed under these conditions in pure CF
4
. In a 13:10 mixture of SF
6
and CF
4
, two strong IRF peaks of the ν
3
modes, shifted to the red relative to the room-temperature fundamentals at 948 cm
^-1
and 1283.2 cm
^-1
, were observed. The peaks are almost equal in height and since both molecules have almost the same ν
3
band intensity, the present result suggests that efficient intermolecular
V-V
energy transfer occurs from excited SF
6
to cold CF
4
molecules. The temporal behavior of the IRF signals under high excitation (
\langlen\rangle \approx 6
) in pure SF
6
exhibits two relaxation times, one of bulk cooling with
\tau_{1} \approx 1
ms and the other of a
V-T
nature with
P\tau_{2} \approx 20 \mu
s . torr. In the mixture, an additional relaxation of the intermolecular
V-V
energy transfer process is observed with
P\tau_{3} \approx 10 \mu
s . torr. The red shift dependence of the IRF peaks on the degree of excitation was also measured and used to examine population distributions, specific IRF transitions, and anharmonicity parameters.