ALBERT

Notes: Renormalization effects of the bath-induced vibronic population transfer on resonant light scattering (RLS) from molecules in condensed phases are theoretically studied based on the Markoffian master equation approach. By using the double space diagram technique, the self-energy originated from the bath-induced vibronic population transfer is analytically solved, and the analytic expressions for the intensities both of the stationary and of the time-resolved RLS spectra are derived. The renormalization effect is analyzed in terms of dimensionless molecular parameters, and model calculations are also performed to confirm theoretical results.

Notes: Effects of the coherence transfer induced by the molecule–heat bath interactions on the ultrashort time-resolved coherent anti-Stokes Raman scattering (CARS) from molecules in liquids are theoretically studied. Based on the perturbative density matrix formalism an expression for the CARS intensity is derived taking into account the coherence transfer between the Raman active vibrational transitions of two molecules in liquids. The coherence transfer constants and dephasing constants are properly incorporated with the aid of Liouville space Feynman diagrams. The structure of the coherence transfer matrix element which expresses the time evolution of the coherence between the relevant transitions is clarified by solving the Master equation with the coherence transfer and dephasing constants in the Markoff approximation. Frequency shifts of the quantum beats appear in the time-resolved CARS as a result of the coherence transfer. A multispherical layer model is adopted in evaluating the coherence transfer effects in liquids in femtosecond time domains. Model calculations of time-resolved CARS spectra have been carried out to demonstrate the coherence transfer effects in both short and long range coherence transfer cases. It is predicted that the quantum beats are amplified in the time-resolved CARS spectra of molecules in liquids in a long range coherence transfer case when there exist differences in the coherence transfer constants between each spherical layer.

Notes: A special case of the x-ray multiple diffraction phenomenon, the Bragg surface diffraction (BSD), has been investigated under lattice damage due to ion implantation in GaAs (001) samples. The BSD profile is very sensitive to the diffraction regime (dynamical or kinematical) and provides information regarding crystalline perfection and lattice strains in both directions—parallel and perpendicular—to the sample surface. Results from grazing-incidence x-ray diffraction and reciprocal space mapping are also reported. © 1997 American Institute of Physics.

Notes: The dephasing and energy relaxation contributions to the line width in infrared (IR) and sum-frequency generation (SFG) spectra of adsorbates are derived from the generalized master equation approach. Expression for the line shift is also obtained. The anharmonic interaction between the adsorbate and the substrate is expanded in a polynomial in terms of the adsorbate and phonon coordinates, and the dephasing is shown to be mainly due to two-phonon processes, while two-phonon, three-phonon or four-phonon processes can contribute to energy relaxation, depending on the relative values of the adsorbate vibrational and the phonon frequencies. The temperature-dependence data of the IR absorption for C(111):H is found to be consistent with the theory, and the large line width for C(111):D can be accounted for by the efficient two-phonon energy relaxation process which is not available for C(111):H due to the higher adsorbate vibrational frequency for C(111):H. © 1997 American Institute of Physics.

Notes: An intensity oscillation of the saturation polar Kerr rotation φK due to interlayer thickness d was observed in Fe(5 A(ring))/Au(d A(ring))/Fe(5 A(ring))(100) and Fe(6 A(ring))/Au(d A(ring))/Fe(6 A(ring))(100) sandwiched films. The periods of the oscillation are about 7–8 and 5–6 monolayers of Au thickness, respectively. The oscillation of φK can be observed only in the photon energy range 2.5–3.8 eV for Fe(6 A(ring))/Au(d A(ring))Fe(6 A(ring)). These phenomena are considered to be closely related to a formation of spin-polarized quantum-well states of the minority Δ1 band in the Au layer sandwiched with two Fe barrier layers. The φK peak positions and oscillation period do not correspond exactly to those of the change in the in-plane saturation field Hs.

Notes: General expressions for internal conversion (IC) rate constant calculations have been derived by taking into account displacements, distortions, and rotation (mixing) of normal modes. The electronic part of the rate constant has been computed through the ab initio calculations of vibronic coupling. The corresponding expressions for the simplest two-mode case as well as for the general n-mode case have been derived. We demonstrate the effect of rotated (mixed) normal modes on the IC rate constants based on a model consisting of one promoting and two mixed modes. The dynamics of excited states of C2H4 has been investigated based on the internal conversion mechanism. The calculated rate of internal conversion show that the lifetimes of the excited π–3p and π–π* states of C2H4 are on the picosecond scale. We predict that if the molecule is excited to a Rydberg π–3p state, it relaxes to the ground state via the cascade mechanism, π–3p→π–3s(1B3u)→π–π*(1B1u)→1Ag. © 1998 American Institute of Physics.

Notes: Time-resolved pump–probe spectra of 1,1′,3,3,3′,3′-hexamethyl-4,4′,5,5′-dibenzo-2,2′indotricarbocyanine (HDITC), a cyanine dye, in ethylene glycol are obtained using 11 fs and 90 fs duration pulses and analyzed in order to study its potential energy surfaces and vibrational dynamics. Ten oscillatory frequencies ranging from 30 cm−1 to 1400 cm−1 are observed in the 11 fs duration wavelength-resolved pump–probe measurements. They are assigned as fundamental vibrational frequencies of HDITC. The relative displacements of the equilibrium position between electronic excited and ground states along the resolved ten vibrational modes are determined through the wavelength dependence of the oscillatory amplitude. After considering the contributions of the ten vibrational modes, it is found that most of the Stokes shift and the early fast decays of the pump–probe signals are due to relaxation along the low frequency overdamped modes of the chromophore. The overdamped modes are characterized by the 90 fs pump–probe signals with the excitation at the red edge of the absorption band. © 1999 American Institute of Physics.

Notes: We construct a microscopic model to describe the excited states of poly(2-methoxy, 5-(2′-ethylhexoxy)-p-(phenylenevinylene) in thin film. Within this model, we deduce that in the high energy region, the nature of excited states in the film is very similar to the species observed in solution phase. Moreover, we propose that the decay process of these excited states involves energy transfer, vibrational relaxation, and dissipation simultaneously, in contrast to the usual argument that assumes exciton migration occurs after vibrational motion reaches thermal equilibrium. As a result, the simulation of time-resolved photoluminescence spectra is in agreement with the experiment. © 2001 American Institute of Physics.

Notes: Experimental and theoretical results are combined to show that vibrationally excited C2H radicals undergo photodissociation to produce C2 radicals mainly in the B 1Δg state. Infrared (IR) emissions from the photolysis of acetylene with a focused and unfocused 193 nm excimer laser have been investigated using step-scan Fourier transform infrared (FTIR) emission spectroscopy at both low and high resolution. With an unfocused laser, the low-resolution infrared emission spectra from the C2H radicals show a few new vibrational bands in addition to those previously reported. When the laser is focused, the only emissions observed in the 2800–5400 cm−1 region come from the electronic transitions of the C2 radicals. Most of the emissions are the result of the B 1Δg→A 1Πu transition of C2 although there are some contributions from the Ballik–Ramsay bands C2(b 3Σg−→a 3Πu). A ratio of [B 1Δg]/[b 3Σg−]=6.6 has been calculated from these results. High quality theoretical calculations have been carried out to determine what kind of ratio could be expected if the photodissociation products are formed solely by adiabatic dissociation from the excited states of C2H. To accomplish this, the geometries of different electronic states of C2H (X 2Σ+, A 2Π, 3–6 2A′, and 2–5 2A″) were optimized at the complete active space self consistent field [CASSCF(9,9)/6-311G**] level. The calculated normal modes and vibrational frequencies were then used to compute Franck–Condon factors for a variety of vibronic transitions. In order to estimate the oscillator strengths for transitions from different initial vibronic states of C2H, transition dipole moments were computed at different geometries. The overall Franck–Condon factor for a particular excited electronic state of C2H is defined as the sum of Franck–Condon factors originating from all the energetically accessible vibrational levels of C2H(X,A) states. The adiabatic excitation energies were calculated with the multi-reference configuration interaction/correlation-consistent polarized valence triple zeta [MRCI(9,9)/cc-PVTZ] method. The overall Franck–Condon factors were then multiplied by the corresponding oscillator strengths to obtain the total absorption intensities characterizing the probabilities for the formation of different excited states. Then, the excited states of C2H were adiabatically correlated to various electronic states of C2 (B 1Δg, A 1Πu, B′ 1Σg+, c 3Σu+, and b 3Σg−) to predict the photodissociation branching ratios from the different states of C2H, such as X(0,ν2,0), X(0,ν2,1), A(0,0,0), and A(0,1,0). For C2H produced by 193 nm photodissociation of acetylene, the calculations gave the following B:A:B′:b:c branching ratios of 38:32:10:14:6. This means that the theoretical branching ratio for the [B 1Δg]/[b 3Σg−] is 2.7, which is in excellent agreement with experiment. © 2001 American Institute of Physics.