Photodissociation of methyl iodide
Senior Chemist and Department Head Stephen T. Pratt (CSE) has published a paper in The Journal of Physical Chemistry A on photodissociation of methyl iodide.
The photodissociation of polyatomic molecules often results in complex behavior that is reflected in product branching fractions, state distributions, and angular distributions.
Even “simple” systems can display non-intuitive behavior that reflects the multidimensional character of the relevant potential surfaces. Such behavior places a high value on well-characterized prototypical systems for which the detailed dynamical processes are understood.
We have determined the I 2P3/2 and 2P1/2 branching fractions following the photodissociation of methyl iodide (CH3I) via a number of vibronic bands associated with the (2E3/2)6s Rydberg state at excitation wavelengths between 201.2 nm and 192.7 nm. Vacuum ultraviolet light at 118.2 nm was used to ionize both the product iodine atoms and the methyl radical co-fragments, and velocity map ion imaging was used to determine the product translational energy distributions and angular distributions. The known relative photoionization cross sections for I 2P3/2 and 2P1/2 at 118.2 nm were used to determine the corresponding branching fractions.
The results extend our earlier work at 193 nm [Xu et al. J. Chem. Phys. 2013, 139, 214310], and complement the closely related work of González et al. [J. Chem. Phys. 2011, 135, 021102]. We find that for most of the excited vibronic levels of the B state studied, the I 2P3/2 branching ratio is small, but non-zero, and that this channel is associated with internally excited CH3 radicals. The results are discussed in relation to the recent theoretical results of Alekseyev et al. [J. Chem. Phys. 2011, 134, 044303].
Hong Xu and Stephen T. Pratt, “Photodissociation of Methyl Iodide via Selected Vibrational Levels of the B (2E 3/2)6s Rydberg State,” The Journal of Physical Chemistry A, Just Accepted Manuscript. DOI:10.1021/acs.jpca.5b00860, Published May 6, 2015.