State-selective photodissociation dynamics of alkyl iodides using REMPI and translational spectroscopy

Abstract

Photofragment Translational Spectroscopy of n-Butyl Iodide at 277 and 304 nm: Polarization Dependence and Energy Partitioning Photodissociation of $n-C_4H_9I$ at excitation wavelengths of 277 and 304 nm has been studied utilizing state-selective photofragment translational spectroscopy. The quantum yields of the $I^*(^2P_{1/2}$) at these wavelengths are determined to be 0.61 and 0.14, respectively. The anisotropy parameters observed at 277 nm are $\overline{β}(I)$ = 1.6 ± 0.1 for the ground state $I(^2P_{3/2})$ and $\overline{β}(I^{*})$ = 0.9 ± 0.1 for the excited state $I^{*}$. The results are interpreted in terms of dual path formation of iodine atoms from two different excited $^3Q_0$ and $^1Q_1$ states, i.e., a direct and an indirect dissociation via curve crossing. The $\overline{β}(I)$ (= 1.9 {±} 0.1) at 304 nm shows that the primary processes for I and $I^{*}$ formation channels proceed dominantly via a parallel transition to $^3Q_0$ state in the long wavelength region of the A band. The translational energy distributions of recoil fragments show that a large fraction of the available energy goes into the internal excitation of the photofragment $( ＜E_{int}＞/E_{avl} \simeq 0.7)$ for both dissociation channels. Energy partitioning in photodissociation of methyl, ethyl and $n$-propyl Iodides at 304 nm The energy partitioning in photodissociation of n-alkyl iodides have been studied at 304 nm. The time-of-flights of iodine atoms are measured to obtain the translational energies of the fragments in the channels leading to I and $I^{*}$ for $CH_3I$, $C_2H_5I$ and $C_3H_7I$. The average energy disposed into the internal mode $(E_{int})$ increases from 17 % for the $I^{*}$ channel of $CH_3I$ to 53 % for the I channel of n-$C_3H_7I$. The methyl radical fragments in $CH_3I$ photolysis have vibrational excitation in the umbrella mode. The distribution peaks at v = 2 for $I^{*}$ and v = 4 for I formation channel, respectively. The observed results are compared w...