Parent–molecule rotational depolarization of photofragment angular momentum distributions: diatomic and polyatomic molecules

Abstract

We extend the A^k_q polarization-parameter model, which describes product angular momentum polarization from one photon photodissociation of polyatomic molecules in the molecular frame [J. Chem. Phys., 2010, 132, 224310], to the case of rotating parent molecules. The depolarization of the A^k_q is described by a set of rotational depolarization factors that depend on the angle of rotation of the molecular axis γ. We evaluate these rotational depolarization factors for the case of dissociating diatomic molecules and demonstrate that they are in complete agreement with the results of Kuznetsov and Vasyutinskii [J. Chem. Phys., 2005, 123, 034307] obtained from a fully quantum mechanical approach of the same problem, showing the effective equivalence of the two approaches. We further evaluate the set of rotational depolarization factors for the case of dissociating polyatomic molecules that have three (near) equal moments of inertia, thus extending these calculations to polyatomic systems. This ideal case yields insights for the dissociation of polyatomic molecules of various symmetries when we compare the long lifetime limit with the results obtained for the diatomic case. In particular, in the long lifetime limit the depolarization factors of the A^k₀ (odd k), Re(A^k₁) (even k) and Im(A^k₁) (odd k) for diatomic molecules vanish; in contrast, for polyatomic molecules the depolarization factors for the A^k₀ (odd k) reduce to a value of 1/3, whereas for the Re(A^k₁) (even k) and Im(A^k₁) (odd k) they reduce to 1/5.