Browsing by Subject "scattering"
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Item Open Access Analysis of femtosecond stimulated Raman spectroscopy of excited-state evolution in bacteriorhodopsin(2010) Niu, Kai; Zhao, Bin; Sun, Zhigang; Lee, Soo-YThe dispersive lines observed in time-resolved femtosecond stimulated Raman spectroscopy (FSRS), using a pair of 809 nm, 3 ps Raman pump, and 840-960 nm ultrashort probe pulse, for the first 500 fs photoisomerization dynamics in the excited state of bacteriorhodopsin, BR* (S-1), created by a prior 500 nm, 35 fs actinic pump pulse, have previously been attributed to Raman initiated by nonlinear emission (RINE). We used four-wave mixing energy level diagrams to describe the FSRS process, which include RINE as a subset, and a 29-mode harmonic oscillator model for BR568 in the calculations. Our calculations showed that FSRS of BR* effectively occurs from the ground vibrational state of each of the observed 800-1800 cm(-1) modes of S-1. The lifetime on S-1 determines the linewidth and decay of the dispersive lines, and is estimated to be similar to 600 fs, comparable to the stimulated emission decay time. The FSRS dipole couplings are from the ground vibrational state of S-1 to high energy vibrational states on BR (S-0), and we place a fast decay lifetime of similar to 100 fs on S-0 which can be attributed to the correlation function from the many unobserved low frequency modes. The FSRS dispersive lines are shown to be due to the inverse Raman scattering term with vertical bar 0 >< 1 vertical bar vibrational coherence on the S-1 surface, and are not due to RINE with vibrational coherence on the S-0 surface. Our calculations show that the RINE process gives rise to broad featureless spectra. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3330818]Item Open Access Photoexcitation of astrophysically important states in Mg-26. II. Ground-state-transition partial widths(2010) DeBoer, RJ; Wiescher, M; Görres, J; Longland, R; Iliadis, C; Rusev, G; Tonchev, APThe level structure of Mg-26 near the neutron-separation energy, which is of interest for s-process nucleosynthesis, was studied at the High Intensity Gamma-Ray Source of the Triangle Universities Nuclear Laboratory using the method of nuclear resonance fluorescence. A nearly monoenergetic and linearly polarized gamma-ray beam was used to scan the excitation energy range from 10.5 to 11.7 MeV. For the five states observed, the total widths and partial widths are determined. Precise measurement of these widths is necessary for the prediction of neutron production for the s-process.Item Open Access Polarization Transfer in the He-4((e)over-right-arrow, e '(p)over-right-arrow)H-3 Reaction at Q(2)=0.8 and 1.3 (GeV/c)(2)(2010) Paolone, M; Malace, SP; Strauch, S; Albayrak, I; Arrington, J; Berman, BL; Brash, EJ; Briscoe, B; Camsonne, A; Chen, J-P; Christy, ME; Chudakov, E; Cisbani, E; Craver, B; Cusanno, F; Ent, R; Garibaldi, F; Gilman, R; Glamazdin, O; Glister, J; Higinbotham, DW; Hyde-Wright, CE; Ilieva, Y; de Jager, CW; Jiang, X; Jones, MK; Keppel, CE; Khrosinkova, E; Kuchina, E; Kumbartzki, G; Lee, B; Lindgren, R; Margaziotis, DJ; Meekins, D; Michaels, R; Park, K; Pentchev, L; Perdrisat, CF; Piasetzky, E; Punjabi, VA; Puckett, AJR; Qian, X; Qiang, Y; Ransome, RD; Saha, A; Sarty, AJ; Schulte, E; Solvignon, P; Subedi, RR; Tang, L; Tedeschi, D; Tvaskis, V; Udias, JM; Ulmer, PE; Vignote, JR; Wesselmann, FR; Wojtsekhowski, B; Zhan, X; E03-104 CollaborationProton recoil polarization was measured in the quasielastic He-4((e) over right arrow, e '(p) over right arrow)H-3 reaction at Q(2) = 0.8 and 1.3 (GeV/c)(2) with unprecedented precision. The polarization-transfer coefficients are found to differ from those of the H-1((e) over right arrow, e '(p) over right arrow) reaction, contradicting a relativistic distorted-wave approximation and favoring either the inclusion of medium-modified proton form factors predicted by the quark-meson coupling model or a spin-dependent charge-exchange final-state interaction. For the first time, the polarization-transfer ratio is studied as a function of the virtuality of the proton.