H. S. Fung

Reaction pathway, energy barrier, and rotational state distribution for Li (2 2PJ)+H2→LiH (X 1Σ+)+H

By using a pump-probe technique, we have observed the nascent rotational population distribution of LiH (v=0) in the Li (2 2PJ) with a H2 reaction, which is endothermic by 1680 cm−1. The LiH (v=0) distribution yields a single rotational temperature at ∼770 K, but the population in the v=1 level is not detectable. According to the potential energy surface (PES) calculations, the insertion mechanism in (near) C2v collision geometry is favored. The Li (2 2PJ)–H2 collision is initially along the 2A′ surface in the entrance channel and then diabatically couples to the ground 1A′ surface, from which the products are formed. From the temperature dependence measurement, the activation energy is evaluated to be 1280±46 cm−1, indicating that the energy required for the occurrence of the reaction is approximately the endothermicity. As Li is excited to higher states (3 2S or 3 2P), we cannot detect any LiH product. From a theoretical point of view, the 4A′ surface, correlating with the Li 3 2S state, may feasibly co...

Fluorescence excitation spectra of the bΠu1, b′Σu+1, cnΠu1, and cn′Σu+1 states of N2 in the 80–100nm region

Fluorescence excitation spectra produced through photoexcitation of N2 using synchrotron radiation in the spectral region between 80 and 100nm have been studied. Two broadband detectors were employed to simultaneously monitor fluorescence in the 115–320nm and 300–700nm regions, respectively. The peaks in the vacuum ultraviolet fluorescence excitation spectra are found to correspond to excitation of absorption transitions from the ground electronic state to the bΠu1, b′Σu+1, cnΠu1 (with n=4–8), cn′Σu+1 (with n=5–9), and c4′(v′)Σu+1 (with v′=0–8) states of N2. The relative fluorescence production cross sections for the observed peaks are determined. No fluorescence has been produced through excitation of the most dominating absorption features of the b-X transition except for the (1,0), (5,0), (6,0), and (7,0) bands, in excellent agreement with recent lifetime measurements and theoretical calculations. Fluorescence peaks, which correlate with the long vibrational progressions of the c4′Σu+1 (with v′=0–8) an...

Temperature effect on the deactivation of electronically excited potassium by hydrogen molecule

Time-resolved fluorescences from varied K excited states are monitored as a function of H2 pressure. According to a three-level model, the rate coefficients of collisional deactivation for the K 6 2S, 7 2S, and 8 2S states at 473 K have been determined to be 4.94±0.15, 5.30±0.15, and 5.44±0.15×10−9 cm3 molecule−1 s−1. In addition, the collision transfer of 2S–2D transition may be derived to be 5.03±0.21, 4.68±0.30, and 4.89±0.36×10−9 cm3 molecule−1 s−1, showing dominance of the 2S-state deactivation processes owing to the effect of near-resonance energy transfer. As the temperature is varied, the activation energies for the collisions of K(6 2S), K(7 2S), and K(8 2S) atoms with H2, respectively, may be estimated to be 5.38±0.33, 4.39±0.16, and 3.23±0.19 kJ/mol. The first two values are roughly consistent with the theoretical calculations of 3.1 and 0.9 kJ/mol in C∞v symmetry predicted by Rossi and Pascale. The obtained energy barriers are small enough to allow for occurrence of the harpoon mechanism, a mo...