In this paper we demonstrate that the vector correlation approach for the study of dissociative photoionization (DPI) of linear molecules enables us to achieve a complete description of molecular photoionization by performing a single experiment using only one state of circularly, or elliptically, polarized light. This is illustrated by the derivation of the complex dipole matrix elements for the benchmark DPI reaction of the NO molecule, where (4σ)−1 inner-valence ionization is induced by left-handed circularly polarized synchrotron radiation at hν=23.65 eV. The importance of electronic correlation for this process is emphasized by comparing the experimental results with multichannel Schwinger configuration interaction calculations. The energy dependence of the transition matrix elements and that of the electronic correlation in the 25–40 eV energy range are illustrated by the calculations and compared with the present results and recent experimental studies at 40.8 eV.

Circular dichroism in the angular distribution of valence photoelectrons emitted from randomly oriented chiral molecules has been observed in experiments that use circularly polarized VUV synchrotron radiation. Photoionization of the outermost carbonyl oxygen lone pair electrons from pure enantiomers of the prototype chiral molecule camphor is shown to have an asymmetry in the forward–backward scattering of photoelectrons (relative to the propagation direction of the light beam) of magnitude approaching 3% at 9.2 eV photon energy. The asymmetry reverses on exchange of either the helicity of the radiation or of the molecular enantiomer, confirming theoretical predictions of an effect that arises in the pure electric-dipole approximation.

Imaging and time-resolved coincidence techniques are combined to determine ion-electron (v-->(i),v-->(e)) velocity correlations in dissociative photoionization of diatomic molecules induced by synchrotron linearly polarized light P-->. The (v-->(i),v-->(e), P-->) vector correlation yields the identification of each process, together with the ( straight theta(e), straight phi(e)) electron emission in the molecule frame for each orientation of the internuclear axis with respect to the polarization. Strong electron emission anisotropies are observed in the NO molecule frame for the parallel and the perpendicular transitions of the NO+hnu(22-25 eV)-->NO+(c(3) Pi)+e-->N+(3P)+O(3P)+e reaction.

The general form of the molecular frame photoelectron angular distributions ͑MFPADs͒ for linear groundstate molecules ionized by linearly polarized light (n ) is reported. A comparison between computed and measured MFPADs as a function of the polar and azimuthal emission angles is presented for photoionization of NO leading to the c 3 ⌸ state of NO ϩ . The importance of the azimuthal dependence of the MFPADs for the determination of the symmetry of the states involved in the excitation and of the underlying photoionization dipole matrix elements is demonstrated.

A new development of electrostatic lenses for ion and/or electron trajectory focusing has been implemented in a double velocity spectrometer which combines time of flight resolved coincidence and imaging techniques using fast position sensitive detectors. Ions and electrons produced by photoionization are extracted from the interaction region by a unique uniform electrostatic field, while the electrostatic lenses create a nonuniform field outside the extraction region. The space focusing reducing the effect of the finite dimensions of the interaction region on one side, and the global bending of the ion and/or electron trajectories preserving the time of flight information on the other side, enable a significant improvement of the resolution of the three measured velocity components for each particle. Such a device is particularly well adapted for the study of vector correlations in dissociative photoionization of simple molecules in the vacuum ultraviolet photon energy range. The gain achieved in the energy resolution of the processes by ion-electron kinetic energy correlation, as well as in the polar and azimuthal angle resolution in the I( e , e ) molecular frame photoelectron angular distributions, is illustrated on the example of dissociative photoionization of the NO molecule.

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.

Dissociative photoionization of H2 induced by VUV linearly polarized synchrotron radiation P has been studied using the (VH+,Ve,P) vector correlation method. The ion–electron kinetic energy correlation diagrams obtained for the three photon excitation energies hν = 20, 28.5 and 32.5 eV enable us to identify and select the dominant dissociative photoionization processes. The Iχ(θe,ϕe) molecular frame photoelectron angular distributions for any orientation χ of the molecular axis with respect to the polarization are reported for direct photoionization of H2 into the H2+(2Σg+) ionic ground state at hν = 20 eV and for the dominant DPI processes involving autoionization of the H2(Q1 1Σu+(1)) and H2(Q2 1Πu(1)) doubly excited states into the H2+(2Σg+) and H2+(2Σu+) continua at hν = 28.5 and 32.5 eV. They show the dominant excitation of a p σu partial wave in autoionization of the Q1(1Σu+(1)) state into the H2+(1s σg) ionic state and that of a d πg partial wave in autoionization of the Q2(1Πu(1)) state into the H2+(2p σu) continuum. A molecular frame forward–backward electron emission anisotropy is observed when ionization takes place at large internuclear distance.

The authors report measured and computed molecular frame photoelectron angular distributions (MFPADs) and recoil frame photoelectron angular distributions (RFPADs) for the single photon ionization of the nonlinear molecule NO2 leading to the (1a2)-1 b 3A2 and (4a1)-1 3A1 states of NO2+. Experimentally, the RFPADs were obtained using the vector correlation approach applied to the dissociative photoionization (DPI) involving these molecular ionic states. The polar and azimuthal angle dependences of the photoelectron angular distributions are measured relative to the reference frame provided by the ion recoil axis and direction of polarization of the linearly polarized light. Experimental results are reported for the photon excitation energies hnu=14.4 and 22.0 eV. Theoretically the authors give expressions for both the MFPAD and the RFPAD. They show that the functional form in the recoil frame, where an average over the azimuthal dependence of the molecular fragments about the recoil direction is made, is identical to that they have earlier found for the DPI experiments performed on linear molecules. MFPADs were then computed using single-center expansion techniques within the fixed-nuclei frozen-core Hartree-Fock approximation. The computed cross sections for ionization to the (1a2)-1 b 3A2 state show a strong propensity for ionization with the polarization of the light perpendicular to the plane of the molecule, whereas the ionization to the (4a1)-1 3A1 state of the ion is of similar intensity for all orientations of the polarization of the light in the molecular frame. These qualitative features of the MFPAD are also evident in the RFPAD. The RFPAD for ionization leading to the (1a2)-1 b 3A2 state is strongly peaked in the perpendicular orientation, whereas the RFPAD for ionization leading to the (4a2)-1 3A1 state is much more nearly isotropic. Comparison between experimental and theoretical RFPADs indicates that the recoil angle for NO+ fragments is approximately 50 degrees relative to the symmetry axis of the initial C2v symmetry of the NO2 molecule in the ionization leading to the (1a2)-1 b 3A2 state and the recoil angle is approximately 120 degrees for the O+ fragment for ionization leading to the (4a1)-1 3A1 state.