AsH3 ultraviolet photochemistry

High-n Rydberg time-of-flight spectroscopy has been used to study the 193.3 nm photolysis of AsH(3). The center-of-mass translational energy distribution for the 1-photon process, AsH(3) + h nu --> AsH(2) + H, P(E(c.m.)), indicates that AsH(2) internal excitation accounts for approximately 64% of the available energy [i.e., h nu - D(0)(H(2)As - H)]. Secondary AsH(2) photodissociation also takes place. Analyses of superimposed structure atop the broad P(E(c.m.)) distribution suggest that AsH(2) is formed with significant a-axis rotation as well as bending excitation. Comparison of the results obtained with AsH(3) versus those of the lighter group-V hydrides (NH(3), PH(3)) lends support to the proposed mechanisms. Of the group-V hydrides, AsH(3) lies intermediate between the nonrelativistic and relativistic regimes, requiring high-level electronic structure theory.