ROTATIONAL ALIGNMENT OF THE CD3 FRAGMENT FROM THE 266-NM PHOTODISSOCIATION OF CD3I

The alignment of CD3 fragments created by photodissociation of CD3I with linearly polarized 266-nm light is characterized by using the ion imaging technique. A linearly polarized probe laser is used for (2 + 1) resonance-enhanced multiphoton ionization (REMPI) of the methyl fragment. The three-dimensional velocity distribution of the state-selected CD3 ion is subsequently "crushed" onto a two-dimensional detector. Each position in the two-dimensional image corresponds to a different methyl fragment velocity, v. By measuring the dependence of the REMPI signal on the angle between the probe laser polarization and the photolysis laser polarization for specific parts of the image, the population n(N,K) and the alignment moments A0(2) and A0(4) of the angular momentum distribution of recoiling CD3 fragments are obtained with respect to v. These velocity-selective alignment moments describe the v.N correlation. The alignment moments extracted for single rotational levels (N,K) indicate that the rotational excitation produced in the photodissociation is about an axis perpendicular to the I-(CD3) axis and that the initial rotation about the C3 axis of the parent is conserved in the methyl fragment. The alignment moments of the fragments recoiling along the direction of the photolysis transition dipole approach the maximum values expected for a purely axial recoil process, i.e., for a methyl fragment in the N,K rotational state, \NKM(N)> = \NKK>.