T. N. Kitsopoulos

Vibrationally resolved spectra of C2–C11 by anion photoelectron spectroscopy

Anion photoelectron spectroscopy has been employed to obtain vibrationally resolved spectra of the carbon molecules C2–C11. The spectra of C−2–C−9 are dominated by linear anion to linear neutral photodetachment transitions. Linear to linear transitions contribute to the C−11 spectrum, as well. From these spectra, vibrational frequencies and electron affinities are determined for the linear isomers of C2–C9 and C11. The term value is also obtained for the first excited electronic state of linear C4. The spectra of C−10 and C−11 show evidence for transitions involving cyclic anions and/or neutrals. Similar types of transitions are identified in the spectra of other smaller molecules, specifically C−6, C−8, and to a lesser extent C−5.

Study of the low‐lying electronic states of Si2 and Si−2 using negative ion photodetachment techniques

The low‐lying electronic states of Si−2 and Si2 were studied using both photoelectron spectroscopy and threshold photodetachment spectroscopy of Si−2 . Our measurements show that the ground state of Si2 is the X 3Σ−g state and that the X 3Σ−g–D 3Πu splitting is 0.083±0.010 eV. Additional spectroscopic constants for the X 3Σ−g, D 3Πu, a 1Δg, b 1Πu and c 1Σ+g states of Si2 were also determined. For Si−2 , the first two electronic states were identified as: 2Πu (Te =0, re =2.207±0.005 A, and ν=533±5 cm−1) and 2Σ+g (Te =0.025±0.010 eV, re =2.116±0.005 A, and ν=528±10 cm−1). The electron affinity for Si2 was found to be 2.176±0.002 eV. Our results provide definitive orderings and splittings for the low‐lying electronic states in both Si2 and Si−2 .

Vibrationally resolved photoelectron spectra of Si−3 and Si−4

Photoelectron spectra of the Si−3 and Si−4 cluster anions have been obtained at 355 and 266 nm. The spectra show transitions to the ground and low‐lying excited electronic states of the neutral clusters. Several of the electronic bands show resolved vibrational structure. The electronic state energies and vibrational frequencies are compared to recent ab initio calculations. The Si−4 spectrum is consistent with the prediction of a planar, symmetric rhombus for the ground state of Si4.

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...

Threshold photodetachment spectroscopy of C5

have obtained vibrationally resolved photoelectron spectra of G&-l1 at a resolution of about 100 cm- ‘. This resolution is comparable to the lowest vibrational frequencies for these clusters, and not all features in the spectra were cleanly resolved. In this Communication, we report a considerably higher resolution (6-10 cm-’ ) photodetachment study of C< using threshold photodetachment spectroscopy.*v9 We observe considerably more vibrational structure than in the CT photoelectron spectrum and obtain evidence for a low-lying excited electronic state of Cs. The threshold photodetachment spectrometer used in this study is described in detail elsewhere.89’0 A beam of cold anion carbon clusters is generated in a laser vaporization/pulsed molecular beam source and is massselected using time of flight. The cluster of interest is then photodetached using a excimer-pumped tunable dye laser operating at 20 Hz, and electrons with near zero kinetic energy (ZEKE) are collected as a function of photon enery. The selective detection of the ZEKE electrons is done using the method developed by Mtiller-Dethlefs

Negative-Ion Photodetachment Studies of Small Silicon and Carbon Clusters

Publisher Summary This chapter discusses negative-ion photodetachment studies of small silicon and carbon clusters. For small silicon and carbon clusters, photodetachment experiments are a good means of obtaining a detailed picture of the low-lying electronic states of both the neutral and anionic structures. Two forms of negative-ion photodetachment spectroscopy are fixed-frequency photoelectron spectroscopy and threshold photodetachment spectroscopy. In a typical experiment, a mass-selected beam of negative cluster ions undergoes photodetachment by laser irradiation. The generated photoelectrons are subsequently energy analyzed, thereby yielding information about the electronic and vibrational states of the neutral. Negative-ion photodetachment is a very powerful spectroscopic probe for clusters, because one can readily mass-select the species of interest prior to spectroscopic interrogation, thus eliminating any uncertainty surrounding the nature of the signal carrier. Furthermore, the selection rules for photodetachment are different from those of optical spectroscopy, thus allowing one to probe electronic states that are dark (forbidden) in absorption or emission experiments. The two photodetachment techniques differ in their electron energy analysis scheme. Although the energy resolution of the threshold photodetachment spectrometer is substantially higher than that of the photoelectron spectrometer, it is the combination of the results from the two instruments that yields the complete picture.

Photoelectron Spectroscopy of Si2

In this report we discuss the photoelectron spectrum of Si 2 − obtained at 355 nm. The spectrum shows a series of transitions to the low-lying triplet states of Si 2 as well as transitions to the higher-lying singlet states. Several possible assignments of the anion and neutral triplet states are presented.