Select Publications

Rotational-resolved pulsed field ionization photoelectron bands for H2+(X 2Σg+, v+=0, 2, 9 and 11)

Abstract: We present here the assignment and simulation of rotational transitions for the H2+(X 2Σg+, v+, 2, 9 and 11) vibronic bands using the Buckingham–Orr–Sichel (BOS) model. The simulation shows that perturbation of PFI-PE rotational line intensities due to near-resonance autoionization decreases as v+ increases. Experimental rotational constants for H2+(X 2Σg+, v+, 2, 9 and 11) are determined with higher accuracy than those obtained in previous He I and Ne I photoelectron studies. In agreement with previous experimental and theoretical investigations, only the ΔN=0 and ±2 rotational branches are observed in the PFI-PE spectrum for H2.

S. Stimsona, Y. -J. Chena, M. Evansa, C. -L. Liaoa, C. Y. Nga, C. -W. Hsub and P. Heimannb

A High Resolution Study of Low Lying Correlation Satellites in Xenon

Abstract: The technique of pulsed field ionization–zero kinetic energy photoelectron spectroscopy, typically applied to the investigation of ionic states of atoms and molecules resulting from single electron excitation, has been used to probe the correlation satellite states of xenon between 23.6–24.7 eV. The resulting spectra show the formation of clearly resolved satellite states with intensities of a similar magnitude to that of the 5s5p6 2S1/2 ionic state. This technique can be extended to other atomic and molecular species to obtain the positions and cross sections for the formation of such states.

R. C. Shiell, M. Evans1, S. Stimson1, C-W. Hsu2, C. Y. Ng1, and J. W. Hepburn

High-Resolution Infrared-Vacuum Ultraviolet Photoion and Pulsed Field Ionization-Photoelectron Methods for Spectroscopic Studies of Neutrals and Cations

Abstract: We show that by scanning the frequency of a single mode infrared (IR) optical parametric oscillator (IR-OPO) laser to excite the molecular species of interest and fixing the frequency of a vacuum ultraviolet (VUV) laser to photoionize the IR excited species, high-resolution IR spectra of polyatomic neutrals can be obtained with high sensitivity. The fact that this IR-VUV-photoion (IR-VUV-PI) method is based on VUV photoionization probe, and thus, allows the identification of the neutral IR absorber, makes it applicable for IR spectroscopy measurements of isotopemers, radicals, and clusters, which usually exist as impure samples. The highly resolved IR-VUV-PI measurements achieved using the single mode IR-OPO laser have made possible the selection of single rovibrational states of CH3X (X = Br and I), C2H4, and C3H4 for VUV-pulsed field ionization-photoelectron (VUV-PFI-PE) measurements, resulting in rovibrationally resolved photoelectron spectra for these polyatomic molecules. These experiments show that the signal-to-noise ratios of the IR-VUV-PI and IR-VUV-PFI-PE spectra obtained by employing the high-resolution IR-OPO laser are significantly higher than those observed in previous IR-VUV-PI and IR-VUV-PFI-PE studies using a low-resolution IR-OPO laser. Further improvement in sensitivity of IR-VUV-PI and IR-VUV-PFI-PE measurements by using the collinear arrangement of IR-VUV lasers and molecular beam is discussed.

Xi Xing, Beth Reed, Mi Kyung Bahng, Peng Wang, Hin Koo Woo, Sun Jong Baek, Chee Shing Lam and Cheuk Yiu Ng