AsH3 Ultraviolet Photochemistry

High-n Rydberg time-of-flight spectroscopy has been used to study the 193.3 nm photolysis of AsH3. The center-of-mass translational energy distribution for the 1-photon process, AsH3 + hv -> AsH2 + H, P(E-c.m.), indicates that AsH2 internal excitation accounts for similar to 64% of the available energy [i.e., hv - D-0(H2As - H)]. Secondary AsH2 photodissociation also takes place. Analyses of superimposed structure atop the broad P(E-c.m.) distribution suggest that AsH2 is formed with significant a-axis rotation as well as bending excitation. Comparison of the results obtained with AsH3 versus those of the lighter group-V hydrides (NH3, PH3) lends support to the proposed mechanisms. Of the group-V hydrides, AsH3 lies intermediate between the nonrelativistic and relativistic regimes, requiring high-level electronic structure theory.