W. L. Glab

Rotationally resolved energy-dispersive photoelectron spectroscopy of H2O: Photoionization of the C̃(0,0,0) state at 355 nm

Measured and calculated rotationally resolved photoelectron spectra for photoionization of low rotational levels of the C^1B_1 Rydberg state of water are reported. This is the first example of rotationally resolved photoionization spectra beyond the special cases of H_2, high-J levels, and threshold spectra. These spectra reveal very nonatomiclike behavior and, surprisingly, the influence of multiple Cooper minima in the photoelectron matrix elements.

Spin-orbit branching ratios for photoionization of the 3dπ gerade states of O2: Evidence for preferential ionization of the Ωc=3/2 core states

We have obtained high‐resolution photoelectron spectra for eight of the ten 3dπ electronic states of O2, using a rotationally resolved, two‐color 2+1′ excitation and ionization scheme. A magnetic bottle photoelectron spectrometer, used to acquire the spectra, provided a resolution sufficient to observe the yields of the individual spin–orbit states of the ground electronic state of the ion. Branching ratios were obtained from the spectra for three different photoionization wavelengths. The overall behavior of the branching ratios for different electronic states can be explained by calculating the core state composition of the intermediate states, taking into account the spin–orbit mixing of Hund’s case (a) basis states, and assuming that electronic states having the core state Ωc=3/2 have a larger photoionization probability than those having an Ωc=1/2 core.

Multichannel quantum defect analysis of the double resonance photoionization series of H2O

A new analysis is presented of the recent photoionization spectrum of H2O, excited by double resonance via several rotational sublevels of the (100) vibrational level of the C(1B1) state. Evidence for a previously unsuspected strong f series indicates significant d orbital contamination of the nominal p orbital in the intermediate state. This is the first report of an f series in the Rydberg state of any asymmetric top. Previous d series analyses of single-photon photoionization spectra terminating on the (100) level of H2O+ are also corrected and extended to a wider range of excited rotational electronic states. The d series appears to contain absent lines, indicative of predissociation. Some lines remain unassigned, but there is no systematic evidence of either s or p series.

Rotationally resolved photoelectron spectroscopy of autoionizing states of water

Rotationally resolved photoelectron spectra are reported for rovibronically state-selected autoionizing levels of water. These photoelectron spectra are helpful for the spectroscopic assignment of the autoionizing levels and provide considerable dynamical information on the mechanisms for the transfer of energy and angular momentum between the ion core and the Rydberg electron. As a result of angular momentum restrictions, photoelectron spectra for J=0 autoionizing levels provide a direct partial wave analysis for the ejected photoelectrons.

Optical–optical double-resonance spectroscopy of autoionizing states of water

Double resonance excitation of vibrationally autoionizing states of the water molecule has been performed for the first time. Tunable, coherent vacuum ultraviolet light was used to excite selected rotational levels of the C 1B1 state with one quantum of symmetric stretch vibrational energy (100), from which (100) Rydberg states were excited with a second dye laser. The Rydberg character of the C 1B1 state leads to strong vibrational selectivity for the (100) states in the second transition; therefore, the resonances due to these states are greatly enhanced compared to the case of direct excitation from the ground state, and spectrally simplified due to the well-defined angular momentum of the intermediate state level. The spectra show unexpected peaks which might be attributable to significant 1-mixing in the C 1B1 state as well as the presence of interloping linear states.

Rotational and vibrational interactions of singlet gerade Rydberg states of H2 near the ionization limit

We have experimentally and theoretically studied the gerade Rydberg states of molecular hydrogen near the ionization limit, detecting ionization and dissociation separately. The spectra in this region show a rich variety of effects due to interactions between Rydberg series with different rotational and vibrational quantum numbers. The states which we have observed are all well described by Hund’s case (d) coupling. We discuss the spectroscopic and dynamic properties of the states as revealed by our experiment, and apply theoretical models to the simulation of several regions of the spectra. These models allowed us to deduce interseries couplings and relative dipole matrix elements, as well as the decay rates for some states.

Dissociation and ionization of vibrationally autoionizing Rydberg states of H2 in a static electric field

We have studied the spectroscopic and dynamic properties of several autoionizing Rydberg states of molecular hydrogen which converge to the vibrationally excited v+=1 state of the ion, in the presence of a static electric field. Using the techniques of multiphoton ionization and time‐of‐flight mass spectrometry, we are able to separately observe the yield of dissociation and ionization after excitation of resolved Stark components of the Rydberg states. The energies of the Stark components can be modeled accurately by an energy matrix diagonalization calculation, when rotational interactions between states converging to different ion rotational states are taken into account. The dynamics of the different states in the Stark manifolds can be partly explained by assuming that they are governing by l mixing of predominantly predissociative s and d states and a dominantly autoionizing p state.

Double-resonance spectroscopy of quasi-linear Rydberg states of water

We have studied quasi-linear autoionizing Rydberg states of the water molecule with three quanta of bending vibration using double-resonance excitation through the quasi-linear (A)3pb2 state. The use of double resonance resulted in vibrational and rotational selectivity which led to simple, easily understood spectra. We have identified and performed an analysis on one ns series and two nd series (σ and π), yielding quantum defects for the series and an improved value of the energy of the ionic state which is the convergence limit for these Rydberg states. At low n, the 4dπ state showed vibronic splitting consistent with the Σ–Δ splitting in the ion core. This splitting vanished at high n as the Rydberg electron uncoupled from the ion core. Comparison of the spectra of bent and linear states in the same energy region displayed the effects of linear-bent interactions on the Rydberg spectrum.

Three-photon excitation of hydrogen Rydberg states

A three-photon process using radiation at 2430 and 3660 A and with a 1s-2s two-photon resonance is used to excite atomic hydrogen from the ground state to Rydberg states of high principal quantum number. Collision-induced ionization is used to monitor the excitation.

Laser induced phase locking of hydrogen plasma striations

Laser induced transient striations of a hydrogen discharge plasma are studied as a function of the ’’detuning’’ of the discharge parameters from the steady‐state oscillatory response conditions. We observed laser induced phase locking of the steady‐state striations.