Chuan-Fan Ding

First experimental photoelectron spectra of superhalogens and their theoretical interpretations

Photoelectron spectra of the MX2− (M=Li, Na; X=Cl, Br, I) superhalogen anions have been obtained for the first time. The first vertical detachment energies (VDEs) were measured to be 5.92±0.04 (LiCl2−), 5.86±0.06 (NaCl2−), 5.42±0.03 (LiBr2−), 5.36±0.06 (NaBr2−), 4.88±0.03 (LiI2−), and 4.84±0.06 eV (NaI2−), which are all well above the 3.61 eV electron detachment energy of Cl−, the highest among atomic anions. Experimental photoelectron spectra have been assigned on the basis of ab initio outer valence Green function (OVGF) calculations. The corresponding theoretical first VDEs were found to be 5.90 (LiCl2−), 5.81 (NaCl2−), 5.48 (LiBr2−), 5.43 (NaBr2−), 4.57 (LiI2−), and 4.50 eV (NaI2−), in excellent agreement with the experimental values. Photodetachment from the top four valence molecular orbitals (2σg22σu21πu41πg4) of MX2− was observed. Analysis of the polestrength showed that all electron detachment channels in this study can be described as primarily one-electron processes.

Photodetachment photoelectron spectroscopy of multiply charged anions using electrospray ionization

A magnetic-bottle time-of-flight (TOF) photoelectron spectrometer, coupled with an electrospray ionization source, has been developed for the investigation of multiply charged anions in the gas phase. Anions formed in the electrospray source are guided by a radio-frequency quadrupole ion guide into a quadrupole ion trap, where the ions are accumulated. A unique feature of this apparatus involves the coupling of a TOF mass spectrometer to the ion trap with perpendicular ion extraction. The ion trap significantly improves the duty cycle of the experiments and allows photodetachment experiments to be performed with low repetition-rate lasers (10–20 Hz). This novel combination makes the photodetachment photoelectron spectroscopy studies of multiply charged anions possible for the first time. Furthermore, the perpendicular extraction of ions, pulsed out of the ion trap, to the TOF mass spectrometer allows the ion energies to be conveniently referenced to ground, simplifying the configuration of the TOF mass sp...

High resolution photoelectron spectroscopy of C60

Vibrationally resolved photoelectron spectra of C60− are reported at three photon energies: 355, 266, and 193 nm. Complicated vibrational structures were observed for the transition to the C60 ground state with both the Ag and Hg modes being active. An extra feature was observed in the energy gap region between the highest occupied and lowest unoccupied orbitals of C60 in the 266 nm spectra only and it was attributed to an autodetachment process. We also report the most accurate measurement of the electron affinity of C60 (2.689±0.008 eV).

Al3Oy (y=0–5) clusters: Sequential oxidation, metal-to-oxide transformation, and photoisomerization

Photoelectron spectra of a series of Al3Oy− clusters (y=0–5) are presented at several photon energies: 532, 355, 266, and 193 nm. The electron affinities and low-lying electronic states of the Al3Oy clusters are reported. The photoelectron spectra clearly reveal a sequential oxidation behavior and how the electronic structure of the clusters evolves from that of a metal cluster at Al3 to that of a complete oxide cluster at Al3O5: Two valence electrons of Al3 are observed to be transferred to each additional O atom until Al3O5, where all the nine valence electrons of Al3 are transferred to the five O atoms. The anion, Al3O5−, which can be viewed as (Al3+)3(O2−)5, is found to be a closed shell cluster, yielding an extremely high electron affinity for Al3O5 (4.92 eV). The electron affinities of the remaining clusters are: 1.90 (Al3), 1.57 eV (Al3O), 2.18 eV (Al3O2), 2.80 eV (Al3O3), and 3.58 eV (Al3O4). An electronic excited state of Al3− is also observed at 0.40 eV above the Al3− ground state. Isomers are o...

Electron tunneling through the repulsive Coulomb barrier in photodetachment of multiply charged anions

Abstract There exists a repulsive Coulomb barrier for electrons in multiply charged anions. Tunneling through this barrier is expected to be important in photodetachment of MCAs. Photodetachment spectra were found to shift to lower binding energies in the tunneling regime. We present a systematic study of the tunneling effect in photodetachment experiments on a series of dianions, − O 2 C(CH2)nCO2− (n=3–6). The observed tunneling effect and spectral shift are explained using WKB approximation based on a model potential with a square well at short range and a repulsive Coulomb potential at long range.

PHOTODETACHMENT PHOTOELECTRON SPECTROSCOPY OF DOUBLY CHARGED ANIONS : S2O82-

A photodetachment photoelectron spectroscopy study of a doubly charged anion (S2O82−) in the gas phase is reported at three photon energies: 193, 266, 355 nm. Adiabatic and vertical electron binding energies of S2O82− were measured to be 1.7±0.2 and 2.2±0.1 eV, respectively. Several excited states were observed for the S2O8− singly charged anion at 193 nm. The repulsive Coulomb barrier that binds multiply charged anions was clearly shown in the detachment spectra of S2O82−. The effects of the Coulomb barrier to the detachment spectra and electron tunneling through the barrier are presented. The barrier height, which is equivalent to the magnitude of the Coulomb repulsion between the two excess charges in S2O82− was estimated to be ∼3 eV.