Electronic-to-Vibrational Energy Transfer from I(5²P_1/2)to I₂(25<v<43)

Abstract

Electronic-to-vibrational energy transfer from 1*(5 2P1/2) to 12(25<u<43) has been observed. I* was created by pulsed laser photolysis of either 12/Ar mixtures at 475 nm or CF31/12/Ar mixtures at 266 nm, while the resulting vibrational distribution of I2 was monitored by laser-induced fluorescence on the 12(B+-X) transition. The experimental results are consistent with a nascent I2 product distribution which is inverted, with a substantial fraction of the I2 molecules formed in u > 30. Roughly 2% of the I* deactivations result in I2(u=40). The rate constants for vibrational relaxation of 12(u=40) by argon, helium, and I2 at room temperature are (7.3 f 0.3) X lo5 s-l torr-l, (1.02 f 0.2) X loe s-' torr-', and (1.8 f 0.4) X lo6 s-l torr-', respect,ively. These results have important implications for the mechanism of I2 dissociation in the chemical oxygen/iodine laser. A chainbranching mechanism consisting of the steps I* + I2 + I + 1,(20<u<40), I2(20<u<40) + @(la) + 21 + 02, and OZ(lA) + I + O2 + I* may be responsible for the dissociation.

Surface aligned photochemistry: Photodissociation of Cl2 and Cl2⋯Cl adsorbed on LiF(001)

“…Since trihalogen molecules have frequently been postulated as intermediates in chemical reactions, [39][40][41][42][43][44][45][46][47][48] we propose that the species giving rise to the fast Cl is the Cl 2¯C l(ad) complex formed at the cold surface as a result of prior partial photodissociation of Cl 2 (ad). A direct spectroscopic evidence for the Cl 2¯C l (Cl 3 ) complex has been provided recently.…”

Mechanism and kinetics of iodine dissociation in COIL

“…This conflict could be resolved by recognizing that several vibrational energy transfer collisions would be needed to relax the initially formed 1 2 (X,v-40) to levels that did not have sufficient energy to be dissociated by a collision with O 2 (a) (I,(X, v<20)). Assuming that the vibrational relaxation rate constant measured by Hall et al 17 corresponded to Av=-I transfer, David et al" 9 used kinetic modeling to show that the vibrational cascade process would not be fast enough to impact the dissociation rate for the conditions of Heidner et al's" 6 experiments. With this insight it was concluded that I2t is the vibrationally excited species, and Heidner et al's"6 model I rate constants were adopted for subsequent simulations of COIL devices.…”

Approximate analytic solution for the dissociation of molecular iodine in the presence of singlet oxygen

“…The resulting iodine atoms are rapidly excited t o the spin orbit state, I(2P1/2), by energy transfer. The dissociation then rapidly accelerates as I* replaces O2(a) as the dominate partner for production of 1; [22][23][24]311. This dissociation process removes at least 2, and sometimes as many as 6-18, OZ(a) molecules per dissociated 12 …”