TWO PHOTON STUDIES OF MATRIX ISOLATED IODINE

Abstract

$^{1}$ W. Fawzy. M. Mackr, J. P. Nicolai and M. C. Heaven, submitted to J. Chem. Phys. $^{2}$ M.A.P. Macler and M. C. Heaven, 14, 43rd Symp. on Molec. Spectrosc. 1988. Work supported by AFOSR under grant 88-0249Author Institution: Department of Chemistry, Emory UniversityVisible laser excitation of matrix isolated iodine produced I.R. emissions that have been resolved into three componenta: the $A(^{3}\Pi_{1}) \to x(^{1}\Sigma_{g}^{+})$ and $A(^{3}\Pi_{2})\to x$ systetas $I_{2}$ and the $1^{2}P_{1/2}\to^{2}P_{3/2} transition.^{1}$ Single photon 193nm excitation of Ar isolated iodine produced a U.V. emission at $380 nm (D(^{3}\Pi_{2g})\to A(^{3}\Pi_{2u}))$ and the I.R. emission $systems.^{2}$ Further studies of visible excitation of concentrated rere-gas iodine matrices revealed A' fluorescence decay curves which were bi-exponential. The fast component ($\tau = 13\pm 2$ ms in Ar) corresponded to radiative decay, while a weak, slow component $(\tau 48\pm 4 ms)$ was thought to be a consequence of energy transfer from shallow-bound metastable electronic states. Sequential 2-photon excitation was used to confirm this hypothesis. In one sales of experiments 532nm pulses were used to excite the metastable states. Population in these stases was monitored by using 308nm pulses to excite to the D state. The metastable state decay lifetime was determined by following the $D'\to A'$ emission intensity as a function of the delay between the 532 and 308nm pulses. A $51\pm 7$ ms lifetime was observed, in excellent agreement with the rate at which population was transfered to the A state. Similar results were obtained with a 193nm pump 308nm probe sequence. In this case initial excitation of D' was followed by radiative relaxation into several valence states. The decay of these states was reflected in the delay dependence of the probe laser fluorescence. Spectral and temporal analyses of these experiments will be discussed