Circular dichroism in photoelectron angular distributions as a probe of atomic and molecular alignment

Abstract

In this paper we show that circular dichroism in photoelectron angular distributions (CDAD) can be used to probe atomic and molecular alignment in the gas phase. Careful choice of photon (left or right circularly polarized) propagation and photoelectron collection directions breaks the cylindrical symmetry of the target, giving rise to dichroic effects. CDAD exists in the electric dipole approximation. We illustrate the sensitivity of CDAD to alignment by considering photoionization of the A 2Σ+ state of NO. Most of the cases of alignment we consider are created by multiphoton absorption while the others, more general, might be created in fragmentation, desorption, etc. The alignment created by n-photon absorption quickly reaches a classical limit which is reflected in the CDAD spectrum. Finally, we show that CDAD is also a sensitive probe of gas phase atomic state alignment by considering photoionization of the 7P3/2 state of cesium created by single photon absorption from the ground state.

Molecular-orbital decomposition of the ionization continuum for a diatomic molecule by angle- and energy-resolved photoelectron spectroscopy. II. Ionization continuum of NO

“…[23][24][25] It is worthwhile to note, however, that in the present study, a complete description of the NO D state has been achieved without measurement of the circular dichroism in PADs ͑CDAD͒. 23,24,[30][31][32] As shown in our previous study, the measurement of CDAD is necessary to determine the signs of phases of dipole-moment matrix elements within the context of the partial-wave theoretical formalism. [23][24][25] In the present analysis, which is based on the molecular-orbital decomposition of the ionization continuum, the CDAD measurement for photoionization of the NO A state alone provides enough experimental constraints for us to determine completely dynamical parameters that describe the photoionization dynamics of the NO A and D states.…”

“…The difference in PADs that result from photoionization with left-and right-circularly polarized light beams constitutes the CDAD. 23,24,[30][31][32] Finally, Fig. 3 shows polar plots of PADs observed from photoionization of the NO D 2 ⌺ ϩ ͑ϭ0, Nϭ18͒ level when both the excitation and the ionization light beams are linearly polarized.…”

“…As discussed previously, the statistical criterion for the acceptability of the fit was that the reduced chi-square value was less than 2. The dynamical parameters listed in Tables I through III 23,24,[30][31][32] The model PADs predicted for each data set by the dynamical parameters in Tables I through III…”

Circular Dichroism in Multiphoton Ionization of Resonantly ExcitedHe+Ions

“…In earlier works (e.g., refs. [6][7][8][9][10][11][12][13][14] and references therein), the study of CD in photoelectron angular distributions revealed detailed information on atomic and molecular ionization, including the realization of a complete experiment, i.e., the determination of the photoionization amplitudes and their phases.…”

Circular dichroism in photoelectron angular distributions from two-color (1+1) REMPI of NO

“…Predictions were made for the magnitude of the CDAD signal for adsorbed atoms and molecules, 8 • 9 and also for gas-phase atoms and molecules whose state alignment is created by the absorption of linearly polarized photons. 10 The first experimental demonstration ofCDAD was recently reported. 13 These theoretical and experimental CDAD studies have illustrated the magnitude of the effect and raise the possibility of employing CDAD as a technique for extracting the alignment of the initial state of the system.…”