Cangshan Xu

Vibrationally resolved photoelectron spectroscopy of silicon cluster anions Sin− (n=3–7)

Photoelectron spectra of Sin− (n=3–7) have been measured at several photodetachment energies. The anions were created using a pulsed discharge source, resulting in considerably colder clusters than in earlier work. As a result, vibrationally resolved spectra were obtained for larger clusters and more electronic states than in previous studies of these species, leading to more accurate electron affinities, term energies, and vibrational frequencies for the ground and excited electronic states of the neutral clusters. The assignments of excited states were aided by ab initio calculations and photoelectron angular distributions.

Photoelectron spectroscopy and zero electron kinetic energy spectroscopy of germanium cluster anions

Anion photoelectron spectra of Ge−n, n=2–15, have been measured using an incident photon energy of 4.66 eV. In addition, the spectra of Ge−2, Ge−3, and Ge−4 have been measured at photon energies of 3.49 and 2.98 eV. From these spectra the electron affinity of the corresponding neutral cluster has been determined. Vibrational frequencies and term values for several electronic states of Ge−2 and Ge−3 have been determined. Vibrational structure in the 3B3u excited state of Ge4 has been resolved using zero electron kinetic energy (ZEKE) photoelectron spectroscopy. The assignment of the spectra of Ge−3 and Ge−4 is facilitated by a comparison to the similar spectra of Si−3 and Si−4, respectively. The spectra of the larger clusters, Ge−n, n=5–15, are characterized by many broad structureless features which indicate the presence of multiple electronic transitions. Several of these were assigned based on comparison with previous ab initio calculations on germanium and silicon clusters.

Study of low‐lying electronic states of ozone by anion photoelectron spectroscopy of O−3

The low‐lying electronic states of ozone are studied using anion photoelectron spectroscopy of O−3. The spectra show photodetachment transitions from O−3 to the X 1A1 ground state and to the five lowest lying electronic states of the ozone molecule, namely the 3A2, 3B2, 1A2, 3B1, and 1B1 states. The geometry of the ozonide anion determined from a Franck–Condon analysis of the O3 X 1A1 ground state spectrum agrees reasonably well with previous work. The excited state spectra are dominated by bending vibrational progressions which, for some states, extend well above the dissociation asymptote without noticeable lifetime broadening effects. Preliminary assignments are based upon photoelectron angular distributions and comparison with ab initio calculations. None of the excited states observed lies below the ground state dissociation limit of O3 as suggested by previous experimental and theoretical results.

PHOTOELECTRON SPECTRA OF THE C2NH- (N=1-4) AND C2ND- (N=1-3) ANIONS

Anion photoelectron spectra of the carbon monohydrides, C2nH− for n=1–4 and C2nD− for n=1–3, have been measured. The spectra were recorded at a wavelength of 266 nm (4.657 eV) and yield electron affinities for each species. The spectra are vibrationally resolved, and some of the vibrational modes in the neutral C2nH(D) radicals are assigned. In addition, photoelectron angular distributions allow one to distinguish between photodetachment transitions to the 2Σ+ and 2Π states of the neutrals. The spectra confirm previous work showing that C2H and C4H have 2Σ+ ground states, while C6H and C8H have 2Π ground states. In addition, we observe the low-lying 2Π or 2Σ+ excited states for all four radicals. The photoelectron angular distributions also serve as a probe of vibronic coupling between the 2Σ+ and 2Π states. These effects are particularly prominent in the C2H− and C4H− spectra.

EVOLUTION OF ELECTRONIC STRUCTURE AS A FUNCTION OF SIZE IN GALLIUM PHOSPHIDE SEMICONDUCTOR CLUSTERS

Abstract Anion photoelectron spectra have been taken of Ga x P y − clusters at a photodetachment wavelength of 266 nm (4.657 eV). Clusters of varying stoichiometry with up to 18 atoms have been investigated. We obtain electron affinities and vertical detachment energies to the ground and low-lying excited states of the neutral clusters. Photoelectron spectra of clusters with 3–5 atoms are compared to previously reported ab initio calculations. Trends in the electron affinities and excitation energies for the larger clusters are discussed.

Photoelectron spectroscopy of C4−, C6−, and C8−

Photoelectron spectra of C4−, C6−, and C8− were obtained at two photodetachment wavelengths, 266 nm (4.657 eV) and 213 nm (5.822 eV). The spectra reveal considerably more electronic and vibrational structure than was seen in previous studies of these species [D. W. Arnold et al., J. Chem. Phys. 95, 8753 (1991)]. Term values for several low-lying excited electronic states of the neutral carbon clusters have been obtained, as well as new vibrational frequencies for the ground and some of the excited electronic states of the neutral clusters. The assignments of excited electronic states were aided by measurements of the photoelectron angular distributions. A new assignment of the vibrational frequencies for C6 is in considerably better agreement with ab initio results than our original assignment.

Anion photoelectron spectroscopy of small indium phosphide clusters (InxP−y; x,y=1–4)

Small indium phosphide clusters having 2–8 atoms are studied using anion photoelectron spectroscopy of InxP−y (x,y=1–4). From these spectra, the electron affinities are determined. Both ground and low‐lying excited electronic states of the neutral clusters are observed. An electronic gap is shown in the even cluster anion spectra.

Study of the low‐lying states of Ge2 and Ge−2 using negative ion zero electron kinetic energy spectroscopy

The low‐lying states of Ge2 and Ge−2 are probed using negative ion zero electron kinetic energy (ZEKE) spectroscopy. The ZEKE spectrum of Ge−2 yields an electron affinity of 2.035±0.001 eV for Ge2, as well as term energies and vibrational frequencies for the low‐lying states of Ge−2 and Ge2. Specifically, we observe transitions originating from the anion 2Πu(3/2) ground state and 3Σ+g excited state (Te=279±10 cm−1) to several triplet and singlet states of Ge2. Term values and vibrational frequencies are determined for the Ge23Σ+g ground state, the low‐lying 3Πu excited state (Te=337 cm−1 for the 2u spin–orbit component), and the somewhat higher lying 1Δg, 3Σ+g, and 1Πu states. We also determine the zero‐field splitting for the X0+g and 1g components of the 3Σ+g state and the splittings between the 2u, 1u, and 0±u spin–orbit components of the 3Πu state. Detailed comparisons are made with Si2 and Si−2.

Spectroscopy of the transition state: Elementary reactions of the hydroxyl radical studied by photoelectron spectroscopy of O−(H2O) and H3O−2

The transition state regions of the OH+OH→O(3P)+H2O and the OH+H2O→H2O+OH reactions are studied by photoelectron spectroscopy of the O−(H2O) and H3O−2 anions and their deuterated analogs. The spectra show resolved vibrational progressions attributed to H‐atom vibrational motion in the unstable neutral complexes formed by photodetachment. The positions and intensities of the peaks change markedly upon isotopic substitution. One‐dimensional Franck–Condon calculations using ab initio potentials for the anion and neutral are used to interpret the peak spacings and intensities, as well as the strong isotopic effects. The results are discussed in the context of previously obtained transition state spectra for heavy+light–heavy reactions.

Anion photoelectron spectroscopy of I2− and I2−⋅Arn(n=1–14, 16, 20) clusters

We report the mass-selected anion photoelectron spectra of I2− and the weakly bound clusters I2−⋅Arn (n=1–14, 16, 20) measured at a photon energy of 4.657 eV. The experiment yields size-dependent vertical and adiabatic detachment energies for the formation of the ground state and five valence-excited states of the neutral cluster, which correspond to the 1∑g+ (X), 3Π2u (A′), 3Π1u (A), 3Π0−u (B′), 1Π1u (B″), and 3Π0+u (B) states of bare I2. The detachment energies are successively blue-shifted with increasing cluster size, indicating a stronger stabilization of the anionic cluster relative to the neutral counterpart. The blue shift is of similar extent for the electronically excited states A′ and A and approximately 10% less for the X state. The I2− and I2−⋅Ar spectra are simulated employing a Franck–Condon analysis, from which we estimate the ion vibrational temperature and determine the I2−–Ar binding energy (D0=53±4 meV). The results are discussed with respect to possible cluster geometries and the evol...