Vector correlations in dissociative photoionization of O2 in the 20–28 eV range. II. Polar and azimuthal dependence of the molecular frame photoelectron angular distribution

Abstract

A combined experimental and theoretical study of the polar and azimuthal dependence of the molecular frame photoelectron angular distributions (MFPADs) for inner-valence-shell photoionization of the O2 molecule into the O2+(B 2Σg−,3 2Πu,c 4Σu−) states is reported. The measured MFPADs, for each orientation of the molecular axis with respect to the linear polarization of the synchrotron radiation, are derived from the spatial analysis of the (VO+,Ve,P) vector correlation, where the nascent ion and electron velocity vectors VO+ and Ve are determined for each dissociative photoionization (DPI) event using imaging and time of flight resolved coincidence technique as described in the companion paper of this series [J. Chem. Phys. 114, 6605 (2001)]. Expressed in the general form of four FLN(θe) functions which contain all the dynamical information about the photoionization processes, they are compared with the MFPADs computed using the multichannel Schwinger configuration interaction method. A very satisfactory agreement is found. When the lifetime of the O2+ ionic states is a significant fraction of the rotational period, the rotational motion of the molecule is included in the quantal derivation of the MFPADs. Measured MFPADs are also reported for the additional DPI process identified in Paper I, and for DPI involving the excitation of the neutral (3 2Πu,4sσg) Rydberg state.

Angular Distributions in Molecular Photoionization

“…(9.23) and (9.24) for linearly and circularly polarized light, with the restriction that ν D 0. The functional form of the RFPAD is therefore identical to that obtained for the MFPAD of a linear molecule [9][10][11]. This same functional form can be obtained for a more general choice of recoil axis in achiral molecules, as long as one averages the RF-PAD over pairs of axes that are connected by a reflection through a symmetry plane of the molecule.…”

“…(9.22)-(9.24) by limiting the sums to include only ν D 0 terms, thus leading to explicit equations for the MFPADs as presented previously for linear molecular systems for ionization by linearly [9], circularly [10], and elliptically [11] polarized light, respectively. It is noteworthy that, out of the five F (L) N,0 functions containing the information extracted from a photoionization experiment performed with elliptically polarized light, four are identical to those obtained from an experiment using linearly polarized light.…”

“…If the dissociation can be modeled as a unimolecular process with lifetime τ then one obtains the functional form of the differential cross-section T i, f for diatomic molecules and, more generally, for linear molecules. Here, the F (L) N,0 are modified to include the effects of rotation that occurs before dissociation, leading to [10] F (L,τ) where the rotational state-specific dipole matrix elements are defined as…”

Circular dichroism in molecular-frame photoelectron angular distributions in the dissociative photoionization ofH2andD2molecules

“…For instance, the multichannel Schwinger configuration-interaction method (MC-SCI) of Lucchese and co-workers [33][34][35] has been shown to provide accurate predictions of molecular-frame photoemission observables measured for a series of molecular targets [20][21][22]30,31]. Density functional theory (DFT) calculations have also been conducted and predict richly structured measured angular distributions from fixed-in-space small polyatomic molecules [36], with recent developments involving time-dependent DFT [37].…”

“…1 takes a remarkably simple general form in the dipole approximation for incident circularly polarized light [20,30] [here μ 0 = 0 is for linearly polarized light and, for instance, μ 0 = +1 indicates lefthanded circularly (LHC) polarized light of positive helicity h = +1]:…”