TWO PHOTON EXCITATION SPECTRA AND ENERGY TRANSFER PROCESSES IN CaCl

$^{1}$ J. A. Coxon, D. A. Ramsay, and D. W. Setser, Can. J, Phys. 53, 1587 (1975).Author Institution: Quantum Institute, University of CaliforniaEnergy transfer between the CaCl $B^{2}\Sigma^{+}$ and $A^{2}\Pi_{1/2,3/2}$ states has been investigated using laser-induced fluorescence. The CaCl was produced either in a heat-pipe oven or in a fllowing metal vapor flame. In spite of the short measured radiative lifetimes (30-40 nsec), efficient electronic and vibrational energy transfer are observed at pressures of less than 1 Torr. Spectra obtained from chemiluminescence, laser-induced photoluminescence and white light photoluminescence indicate the power of comparison techniques in studying energy transfer processes. Comparison of the data between the metal-rich heat pipe measurements and metal-lean flames as a means of mechanism elucidation will be discussed. Photoexcitation and laser photoluminescence spectra obtained with a Rhodamine 6G cw tunable dye laser will be discussed. In particular, dye-laser double resonance experiments which pump first $B^{2}\Sigma^{+} \leftarrow X^{2}\Sigma^{+}$ and then $E^{2}\Sigma^{+} \leftarrow B^{2}\Sigma^{+}$ will be considered

ROTATIONAL ANALYSIS OF THE A2Π−X2Σ+A^{2}\Pi - X^{2}\Sigma^{+} SYSTEM OF SrF

$^{1}$Peter J. Domaille, Timothy C. Steimle, and David O. Harris, J. Mol. Spectrosc. 68, 146 (1977).""Author Institution: Quantum Institute and Department of Chemistry, University of California; Central Research and Development Department, E. I. du Pont de Nemours and CompanyThe excitation spectrum of the $A^{2}\Pi_{r} - X^{2}\Sigma^{+}$ band system of SrF has been measured using tunable cw dye laser excitation spectroscopy. The spectrum has been analyzed to obtain rotational and vibrational constants for the $A^{2}\Pi_{r}$ and $X^{2} \Sigma^{+}$ states. Results from our previous Microwave-Optical Double Resonance measurements for the $X^{2} \Sigma^{+}$ $state^{1}$ were merged with those from this optical analysis to obtain more precise values for the spectroscopic constants. Results of the analysis will be discussed

ROTATIONAL ANALYSIS OF THE B2Σ−X2ΣB^{2}\Sigma-X^{2}\Sigma SYSTEM OF SrF

Author Institution: Quantum Institute and Department of Chemistry, University of CaliforniaLaser excitation spectroscopy has been used to determine rotational and vibrational constants for the $B^{2}\Sigma$ and $X^{2}\Sigma$ states of SrF. The advantages of using this type of spectroscopy to unravel complex spectra will be discussed. The experimental values of the constants were used to obtain an RKR potential from which Franck-Condon factors were calculated and compared to experimentally measured values. Such a comparison shows clear evidence of the heterogeneous electronic perturbation of the $B^{2}\Sigma$ state by the nearby ($\sim$ 2000 $cm^{-1}$) $A^{2}\Pi$ state

MICROWAVE-OPTICAL-DOUBLE-RESONANCE STUDY AND OPTICAL RE-ANALYSIS OF CaF A2Πr−X2ΣA^{2}\Pi_{r}-X^{2}\Sigma BAND

Author Institution: Quantum Institute and Department of Chemistry, University of CaliforniaThe excitation spectrum of $A^{2}\Pi - X^{2}\Sigma$ band system of CaF has been measured using tunable cw dye laser excitation spectroscopy. In order to obtain the precise rotational and spin-rotation coupling constants, the Microwave Optical Double Resonance (MODR) method has been applied to low J transitions. The MODR signals were observed as 1 to 2% increases in the optical fluorescence. The hyperfine splittings of the ground state could not be resolved because of the broad nature of the MODR lines. Using these precise ground state constants, we have reanalyzed the excitation spectrum of $A^{2}\Pi_{r} - X^{2}\Sigma$ system to obtain accurate constants for both states

Hepatitis C Virus NS3 Protease Requires Its NS4A Cofactor Peptide for Optimal Binding of a Boronic Acid Inhibitor as Shown by NMR

AbstractNMR spectroscopy was used to characterize the hepatitis C virus (HCV) NS3 protease in a complex with the 24 residue peptide cofactor from NS4A and a boronic acid inhibitor, Ac-Asp-Glu-Val-Val-Pro-boroAlg-OH. Secondary-structure information, NOE constraints between protease and cofactor, and hydrogen-deuterium exchange rates revealed that the cofactor was an integral strand in the N-terminal β-sheet of the complex as observed in X-ray crystal structures. Based upon chemical-shift perturbations, inhibitor-protein NOEs, and the protonation state of the catalytic histidine, the boronic acid inhibitor was bound in the substrate binding site as a transition state mimic. In the absence of cofactor, the inhibitor had a lower affinity for the protease. Although the inhibitor binds in the same location, differences were observed at the catalytic site of the protease