Photodissociation of the linear Ar-I2 van der Waals complex: velocity-map imaging of the I2 fragment.

Photodissociation of the Ar-I(2) 1:1 linear van der Waals complex is studied over the 490-520 nm region using the velocity-map imaging technique. Molecular iodine, and both the T-shaped and linear Ar-I(2)(X,v(")=0) ground-state complexes absorb strongly in this range, and these transitions access both the bound and dissociative regions of the I(2)(B) state. We measure the angle-speed distribution of vibrationally excited I(2)(B,v(')) state products by resonant 1+1 ionization via the E and f ion-pair states, forming I(2) (+), which is imaged under velocity-mapping conditions. The images show a strong angular anisotropy, which is the same for all excitation energies, spanning from the bound region to above the molecular dissociation limit. The observed angular anisotropy of the I(2) fragments is consistent with a direct dissociation of linear Ar-I(2) complexes promoted to the inner repulsive potential wall of the Ar+I(2)(B,v(')) potential energy surface.