Caroline C. Arnold

Study of the ArBr−, ArI−, and KrI− anions and the corresponding neutral van der Waals complexes by anion zero electron kinetic energy spectroscopy

Three rare gas halide (RgX−) anions, ArBr−, ArI−, and KrI−, and the corresponding open‐shell van der Waals complexes, ArBr, ArI, and KrI, were studied with anion zero electron kinetic energy (ZEKE) spectroscopy. Photodetachment of each anion accesses the three lowest‐lying electronic states (the X1/2, I3/2, and II1/2 states) of the neutral complex. The spectra for each system reveal well‐resolved progressions in the low frequency vibrations of the anion and the three neutral electronic states, providing a detailed spectroscopic probe of the Rg⋅X− and Rg⋅X interaction potentials. The line shapes observed in the ZEKE spectra are analyzed in terms of the line strengths of the underlying rotational transitions. From our data, we construct the potential energy curve for each neutral state as well as for the anion, and these interaction potentials are compared to potentials obtained from scattering and ion mobility experiments.

Study of Si4 and Si4- using threshold photodetachment (ZEKE) spectroscopy

The threshold photodetachment (ZEKE) spectrum of Si4− is presented. Although no transitions to the ground state of Si4 are observed, we obtain detailed information on the anion and several of the low‐lying excited states of neutral Si4. The spectrum shows a long progression of well‐resolved transitions between the D2h 2B2g rhombus anion and ν2 vibrational levels of the first excited D2h 3B3u neutral. The length and spacing of the progression is consistent with ab initio calculations performed by Rohlfing and Raghavachari [J. Chem. Phys. 96, 2114 (1992)], but some of the sequence bands observed within the progression are not. We also observe transitions to the Si4 1B3u state which is found at a lower excitation energy than predicted. The perturbed vibrational structure in this band is attributed to vibronic coupling to a nearby electronic state which is ‘‘dark’’ with respect to ZEKE spectroscopy. The ZEKE spectra are compared to the previously obtained photoelectron spectra of Si4− as well as ab initio cal...

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.

Threshold photodetachment zero‐electron kinetic energy spectroscopy of Si−3

The threshold photodetachment zero‐electron kinetic energy (ZEKE) spectrum of Si−3 is presented and discussed. The spectrum shows well‐resolved vibrational structure. A comparison with several ab initio calculations shows that the spectrum is due to transitions to the 3A’2 (D3h) state of Si3. The symmetric stretch and degenerate e’ frequencies for the Si3 3A’2 state are determined to be 501±10 and 337±10 cm−1, respectively. Additional structure observed in the spectrum suggests that the negative ion is a fluxional, Jahn–Teller distorted species. The ZEKE spectrum shows no evidence for transitions to the 1A1 state of the neutral, which is predicted to lie very close to the 3A’2 state. A comparison of the ZEKE and previously obtained photoelectron spectrum of Si−3 suggests that these two states are close in energy, but that transitions to the singlet state are very weak in the ZEKE spectrum.

Study of C6− and C6 with threshold photodetachment spectroscopy and autodetachment spectroscopy

The C6− anion and C6 neutral have been studied using both threshold photodetachment (zero electron kinetic energy) spectroscopy and autodetachment spectroscopy of C6−. The threshold photodetachment spectrum yields the electron affinity of linear C6 to high accuracy, along with the three symmetric stretch frequencies for linear C6 and the spin–orbit splitting in the ground 2Πu state of the anion. Two of the symmetric stretch frequencies are significantly lower than previous ab initio predictions. A simple model force field is used to calculate stretching force constants and estimate bond length changes between the anion and neutral. In addition, using autodetachment spectroscopy, we have located an excited electronic state of C6− that lies 43 cm−1 below the detachment threshold. This state is very similar in geometry to neutral C6. Excited vibrational levels of this state autodetach with rates that depend strongly on the available autodetachment channels. The excited state is tentatively assigned to a vale...

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.

Study of the I·CO2 van der Waals complex by threshold photodetachment spectroscopy of I–CO2

Photodetachment of the I–CO2 anion accesses the three lowest-lying electronic states of the I·CO2 van der Waals complex. High-resolution threshold photodetachment (ZEKE) spectroscopy reveals progressions in the low-frequency C–I van der Waals stretch in each electronic state, providing a detailed spectroscopic probe of the interaction between a halogen atom and a closed-shell molecule. From our data, we construct one-dimensional potential-energy functions for each neutral state as well as for the anion, and these are compared to rare-gas–halogen and rare-gas–halide potentials.

Reply to Comment on: Study of C−6 and C6 with threshold photodetachment spectroscopy and autodetachment spectroscopy

This reply offers further support for the assignments of the vibrational frequencies of C6 made in our original paper [C. C. Arnold, Y. Zhao, T. N. Kitsopoulos, and D. M. Neumark, J. Chem. Phys. 97, 6121 (1992)]. Two of our experimental frequencies are quite different from the corresponding ab initio values, and the resolution of this discrepancy clearly requires further theoretical work.