Kinetic Energy Pulsed Field Ionization Research Articles

Photoelectron studies on vibronic coupling in pyrazine

Ionization pathways from the S(1) and T(1) states of pyrazine are investigated using one- and two-photon ionization of the excited state by both resonance enhanced multiphoton ionization photoelectron spectroscopy and zero electron kinetic energy pulsed field ionization techniques. For the triplet manifold, we show that two-photon ionization of T(1) is enhanced by a vibronically induced resonance for which we determine the inducing mode and the nature of the intermediate state, as well as the (3)3s(n(-1)) Rydberg state. For the singlet manifold, we identify the mode responsible for the vibronically induced intensity of a 3p Rydberg state that was previously found to greatly perturb the 1+2(') photoelectron spectrum of S(1) by a resonance at the two-photon level.

Biexponential decay of peak intensities in the zero electron kinetic energy pulsed field ionization of HCl

Calculations of both the effects of spin-orbit autoionization and electric field reproduce the biexponential decay observed previously in the zero electron kinetic energy-pulsed field ionization of HCl.

ZEKE-PFI spectroscopy of 1:1 complexes of sodium with water and ammonia

ZEKE-PFI (zero kinetic energy pulsed field ionization) photoelectron spectra of the Na(H 2O), Na(D 2O), Na(NH 3), and Na(ND 3) complexes are reported. Spectra of all four complexes were obtained by single-photon ionization, and, for the Na(NH 3) and Na(ND 3) complexes, by two-color (1 + 1′) photoionization as well, with the à 2E state serving as the intermediate resonance. Improved values for the ionization energies (IE) and intermolecular vibrational frequencies of the complexes were determined. The single-photon ZEKE-PFI spectra show transitions only between states of the same vibrational symmetry, in accord with the selection rule for allowed electronic transitions. Some of the two-color ZEKE-PFI spectra, however, show strong transitions between states of different vibrational symmetry which we attribute to vibronic coupling in the intermediate state.

Two-photon ionization and dissociation of ethyl iodide

Both spin–orbit states of C2H5I+, the X̃1 2E1/2 and the X̃2 2E1/2 electronic states, are studied by one-color two-photon ionization of ethyl iodide, utilizing the zero kinetic energy pulsed field ionization (ZEKE-PFI) photoelectron technique. Compared with conventional photoelectron data the two-photon spectra exhibit a more extensive vibrational structure mainly involving the C–I stretching and the C–C–I bending modes. This additional vibrational excitation in the two-photon spectra is discussed in terms of mode selective resonance enhancement by the dissociative Ã-state continuum. Accurate values for the vibrational frequencies and the ionization energies are obtained. The appearance of nontotally symmetric modes in the two-color ZEKE spectra is reported.

Electron transfer in high n Rydberg states

A model is developed to determine the rate of electron transfer between high n molecular Rydberg states and ions of the same species under zero kinetic energy pulsed field ionization (ZEKE-PFI) experimental conditions. A simple hydrogenic model is used considering the two particles to be at rest with respect to each other. The results of accurate calculations for the u–g splitting in H+2 at low principal quantum numbers (separated atom) as a function of radius are extrapolated to large values of n relevant to typical ZEKE-PFI experimental conditions and used to determine the rate of electron transfer. Radius ≊5n2 is arrived at as a simple expression to estimate the radius for a charge transfer rate of ≊108 s−1 for lowest energy members of the Stark manifold (the fastest). Expressions are derived for other members of the manifold. Results are compared with the recent observation of 3% charge transfer in a ZEKE-PFI experiment by Alt et al.

Zero kinetic energy photoelectron spectroscopy of Rydberg excited molecular iodine

Two color (2+1′) zero kinetic energy pulsed field ionization (ZEKE-PFI) spectra of I2 ionized via a number of gerade Rydberg excited states have been recorded for the first time. Ionization into both X 2Π3/2,g and X 2Π1/2,g spin–orbit ionic substates was achieved by selective excitation of Rydberg states having the appropriate spin–orbit ionic core. Adiabatic ionization energies have been determined as 75 069±2 cm−1 for the X 2Π 3/2,g state and 80 266±2 cm−1 for the X 2Π1/2,g state with ωe values for the two states determined as 240±1 and 229±1 cm−1, respectively. The ZEKE-PFI spectra recorded for the lower spin–orbit state exhibit non-Franck–Condon behavior which has been interpreted in terms of an autoionization mechanism. The ZEKE-PFI technique has also been used to probe the extent of Rydberg and ion-pair character in a strongly mixed Rydberg/ion-pair state.

Resonance enhanced multiphoton ionization photoelectron spectroscopy and pulsed field ionization via the F 1Δ2(v′=0) and f 3Δ2(v′=0) Rydberg states of HCl

In this paper, we report the first rotationally resolved one- and two-color resonance enhanced multiphoton ionization photoelectron spectroscopy (REMPI-PES) study of the HCl molecule. The agreement between our experimental branching ratios and theoretical investigations is excellent. We also report the first zero kinetic energy pulsed field ionization (ZEKE-PFI) experiments carried out in a ‘‘magnetic bottle’’ electron spectrometer. A direct comparison is made between ZEKE-PFI and REMPI-PES spectra for ionization via several rotational levels of the F 1Δ2(v′=0) and f 3Δ2(v′=0) Rydberg states of HCl. Large differences in both the spin–orbit and rotational branching ratios are found between the ZEKE-PFI and REMPI-PES spectra. These differences can be understood qualitatively on the basis of rotational and spin–orbit autoionization mechanisms.