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The single-photon, photoelectron-photoion coincidence spectrum of N2 has been recorded at high (~1.5 cm-1) resolution in the region between the N2+ X ²Σg+, v+ = 0 and 1 ionization thresholds by using a double-imaging spectrometer and intense vacuum-ultraviolet light from the Synchrotron SOLEIL. This approach provides the relative photoionization cross section, the photoelectron energy distribution, and the photoelectron angular distribution as a function of photon energy. The region of interest contains autoionizing valence states, vibrationally autoionizing Rydberg states converging to vibrationally excited levels of the N2+ X ²Σg+ ground state, and electronically autoionizing states converging to the N2+A ²Π and B ²Σu+ states. The wavelength resolution is sufficient to resolve rotational structure in the autoionizing states, but the electron energy resolution is insufficient to resolve rotational structure in the photoion spectrum. A simplified approach based on multichannel quantum defect theory is used to predict the photoelectron angular distribution parameters, β, and the results are in reasonably good agreement with experiment. [ABSTRACT FROM AUTHOR]

The single-photon, photoelectron-photoion coincidence spectrum of N2 has been recorded at high (~1.5 cm-1) resolution in the region between the N2+ X ²Σg+, v+ = 0 and 1 ionization thresholds by using a double-imaging spectrometer and intense vacuum-ultraviolet light from the Synchrotron SOLEIL. This approach provides the relative photoionization cross section, the photoelectron energy distribution, and the photoelectron angular distribution as a function of photon energy. The region of interest contains autoionizing valence states, vibrationally autoionizing Rydberg states converging to vibrationally excited levels of the N2+ X ²Σg+ ground state, and electronically autoionizing states converging to the N2+A ²Π and B ²Σu+ states. The wavelength resolution is sufficient to resolve rotational structure in the autoionizing states, but the electron energy resolution is insufficient to resolve rotational structure in the photoion spectrum. A simplified approach based on multichannel quantum defect theory is used to predict the photoelectron angular distribution parameters, β, and the results are in reasonably good agreement with experiment. [ABSTRACT FROM AUTHOR]

Resonantly enhanced multiphoton ionization via the EF¹Σg+, v' = 6 double-well state has been used to probe the energy region below the third dissociation limit of H2 where several high vibrational levels of the 4¹Σu+ state are expected. Theoretical ab initio potential energy curves for this state predict a deep inner well and shallow outer well where vibrational levels above v = 8 are expected to exhibit the double-well character of the state. Since the 4¹Σu+ state has f -state character, transitions to it from the ground state are nominally forbidden. However, the d character of the outer well of the EF1S+ g state allows access to this state. We report observations of transitions to the v = 9-12 levels of the 4¹Σu+ state and compare their energies to predicted energies calculated from an ab initio potential energy curve with adiabatic corrections. Assignments are based on measured energies and linewidths, rotational constants, and expected transition strengths. The amount of agreement between the predicted values and the observations is mixed, with the largest discrepancies arising for the v = 9 level, owing to strong nonadiabatic electronic mixing in this energy region. [ABSTRACT FROM AUTHOR]

Resonantly enhanced multiphoton ionization via the EF¹S+g, U' = 6 double-well state has been used to probe the energy region below the third dissociation limit of H2 where several high vibrationallevels of the 4¹S+u state are expected. Theoretical ab initio potential energy curves for this state predict a deep inner well and shallow outer well where vibrational levels above u = 8 are expected to exhibit the double-well character of the state. Since the 4¹S+u state has f-state character, transitions to it from the ground state are nominally forbidden. However, the d character of the outer well of the EF¹S+g state allows access to this state. We report observations of transitions to the u = 9-12 levels of the 4¹S+u state and compare their energies to predicted energies calculated from an ab initio potential energy curve with adiabatic corrections. Assignments are based on measured energies and linewidths, rotational constants, and expected transition strengths. The amount of agreement between the predicted values and the observations is mixed, with the largest discrepancies arising for the u = 9 level, owing to strong nonadiabatic electronic mixing in this energy region. [ABSTRACT FROM AUTHOR]

Double-resonance laser spectroscopy via the EF ¹Σg+ ν' = 6, J' = 0-2 state was used to probe the high vibrational levels of the B"B ¹Σu+ state of molecular hydrogen. Resonantly enhanced multiphoton ionization spectra were recorded by detecting ion production as a function of energy using a time of flight mass spectrometer. New measurements of energies for the ν = 51-66 levels for the B"B state of H2 are reported, which, taken with previous results, span the ν = 46-69 vibrational levels. Results for energy levels are compared to theoretical close-coupled calculations [L. Wolniewicz, T. Orlikowski, and G. Staszewska, J. Mol. Spectrosc. 238, 118-126 (2006)]. The average difference between the 84 measured energies and calculated energies is -3.8 cm-1 with a standard deviation of 5.3 cm-1. This level of agreement showcases the success of the theoretical calculations in accounting for the strong rovibronic mixing of the ¹Σu+ and ¹πu+ states. Due to the ion-pair character of the outer well, the observed energies of the vibrational levels below the third dissociation limit smoothly connect with previously observed energies of ion-pair states above this limit. The results provide an opportunity for testing a heavy Rydberg multi-channel quantum defect analysis of the high vibrational states below the third dissociation limit. [ABSTRACT FROM AUTHOR]

The ionization of a beam of H2 Rydberg molecules in collision with a metal surface (evaporated Au or Al) is studied. The Rydberg states are excited in an ultraviolet–vacuum ultraviolet double-resonant process and are state selected with a core rotational quantum number N+=0 or 2 and principal quantum numbers n=17–22 (N+=2) or n=41–45 (N+=0). It is found that the N+=0 states behave in a very similar manner to previous studies with atomic xenon Rydberg states, the distance of ionization from the surface scaling with n2. The N+=2 states, however, undergo a process of surface-induced rotational autoionization in which the core rotational energy transfers to the Rydberg electron. In this case the ionization distance scales approximately with ν02, the effective principal quantum number with respect to the adiabatic threshold. This process illustrates the close similarity between field ionization in the gas phase and the surface ionization process which is induced by the field due to image charges in the metal surface. The surface ionization rate is enhanced at certain specific values of the field, which is applied in the time interval between excitation and surface interaction. It is proposed here that these fields correspond to level crossings between the N+=0 and N+=2 Stark manifolds. The population of individual states of the N+=2, n=18 Stark manifold in the presence of a field shows that the surface-induced rotational autoionization is more facile for the blueshifted states, whose wave function is oriented away from the surface, than for the redshifted states. The observed processes appear to show little dependence on the chemical nature of the metallic surface, but a significant change occurs when the surface roughness becomes comparable to the Rydberg orbit dimensions. [ABSTRACT FROM AUTHOR]

Two-color laser-induced grating spectroscopy (TC-LIGS) via the A 2Σ+, v’=0 state has been used to study the B 2Π, v=28 and L 2Π, v=8 valence states and the Q 2Π, v=0 5pπ Rydberg state of NO. Energies for previously unobserved or unresolved transitions to the perturbed L 2Π1/2,3/2, v=8 and Q 2Π1/2,3/2, v=0 states are reported for the first time. The interaction between these states is reconsidered in light of the new assignments. A comparison of different detection methods made for the B 2Π1/2,3/2, v=28←A 2Σ+, v’=0 transitions demonstrates the ability of TC-LIGS to detect states that are difficult to detect by ionization or fluorescence-dip detection. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A high-resolution, state-selective investigation of the decay of (X 2Σg+)np, v’≥9 Rydberg states of H2 into the H(1s)+H(3l) and H(1s)+H(4l) dissociation continua has been performed. The (X 2Σg+)np Rydberg states were excited by double-resonance excitation via the E,F 1Σg+, v=6, J=0 and 1 states, and the H(3l) and H(4l) dissociation products were detected by monitoring the energy-resolved photoelectrons produced by nonresonant photoionization of the fragments. The energy region of interest (138 800–140 000 cm-1) includes the X 2Σg+, v+=9, N+=0–3 ionization thresholds, the H(1s)+H(4l) dissociation threshold, and the H++H- ion-pair threshold. Evidence of both direct and indirect dissociation involving both singly and doubly excited electronic states is observed. Comparisons to the previously observed X 2Σg+, v+=8 constant-ionic-state photoelectron spectrum and the ion-pair spectrum observed in the same energy region reveal strong competition between the ionization and dissociation processes through both rovibrational and electronic interactions. [ABSTRACT FROM AUTHOR]

The alignment of the E,F 1Σ+g, vE=1 state of H2 produced by two-photon excitation from the X 1Σ+g, v‘=0 ground state was investigated using two different techniques. First, in a single-color experiment, photoelectron angular distributions were measured for the two-photon resonant, three-photon ionization of H2 via the Q(0) and Q(1) transitions to the E,F 1Σ+g, v’E=1 state. The photoelectron angular distributions are consistent with an unaligned E,F 1Σ+g, vE=1, J’=1 state. Second, in a two-color experiment, the photoionization spectra of several vibrationally autoionizing (X 2Σ+g)np, v=1 Rydberg states excited from the v’E=1, J’=1 level of the E,F 1Σ+g state were measured as a function of the relative polarizations of the pump and probe beams. The polarization dependence of the relative intensities of the P(1) and Q(1) transitions was used to determine the alignment of the E,F 1Σ+g, vE=1, J’=1 state produced by the pump laser. Consistent with the angular distribution measurements, the polarization results indicate that the populations in the M’=0 and M’=±1 levels of the E,F 1Σ+g, v’E=1, J’=1 state are equal, within the experimental uncertainty of 15%. [ABSTRACT FROM AUTHOR]

Photoelectron spectra of vibrationally autoionized (X 2Σ+g)np, v=1,2 Rydberg states of H2 were obtained by using an optical–optical double-resonance technique. The spectra were obtained by using a hemispherical electrostatic electron energy analyzer that had sufficient resolution to determine the rotational state distributions of the H+2 ions. The ionization process occurred in a magnetic and electric field-free region. All of the results are consistent with the assumptions that the photoelectrons are ejected as p waves and that spin effects are negligible. This is in sharp contrast to our earlier results obtained by using a magnetic bottle electron spectrometer, in which the ionization process occurred in a 0.5–1.0 T magnetic field [J. L. Dehmer et al., J. Chem. Phys. 90, 6243 (1989)]. It is concluded that the magnetic field can significantly modify the rotational distributions observed for vibrational autoionization. The implications of this conclusion are discussed, with particular attention to other experiments performed with the magnetic bottle spectrometer. [ABSTRACT FROM AUTHOR]