Photodissociation dynamics of ClO radicals at 248 nm

The photodissociation of ClO radicals produced photolytically in a molecular beam was studied at 248 nm using photofragment translational energy spectroscopy, Excitation into the ClO absorption continuum to the blue of the structured region of the ClO(A(2) Pi <-- X(2) Pi) spectrum led to dominant (similar to 97%) formation of Cl(P-2(3/2)) + O(D-1(2)) with negligible (<0.5%) production of Cl(P-2(1/2)) + O(D-1(2)). The photofragment anisotropy parameter (beta) was measured to be 1.2 +/- 0.2 for the dominant Cl(P-2(3/2)) + O(D-1(2)) channel, significantly less than the limiting value of 2.0 expected for the parallel ClO (A(2) Pi <-- X(2) Pi) transition. This indicates that, in the ClO continuum region near 248 nm, absorption to an as yet uncharacterized electronic state [probably B((2) Sigma(+))] carries similar to 30% of the oscillator strength. This state, like ClO(A(2) Pi), dissociates primarily to Cl(P-2(3/2)) + O(D-1(2)). A second minor photodissociation channel, accounting for approximately 3% of the ClO absorption cross section, leads to production of Cl(P-2(1/2)) + O(P-3(J)). As in the photodissociation of ClO below the A(2) Pi convergence limit, this minor channel probably involves predissociation of ClO(A(2) Pi) by one or more as yet uncharacterized repulsive electronic surfaces.