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Deposition and annealing behaviors of Al atoms on rough Cu (111) surface were investigated on the atomic scale by three-dimensional classical molecular dynamics simulation. The rough Cu surface was modeled by depositing 5 ML of Cu on Ta (011) substrate. Most Al atoms deposited on the rough Cu surface placed on the atomic steps, preserving the major features of the surface during Al deposition. This behavior was discussed in terms of the smaller barrier of the surface diffusion than Ehrlich–Schwoebel barrier of Al on Cu (111) surface. By annealing at 700 K, significant intermixing between Al and Cu rapidly occurs with decrease in the surface roughness. This behavior reveals that the exchange process of Al with substrate Cu dominates during the initial stage of high temperature annealing. [ABSTRACT FROM AUTHOR]

Surface structure evolution during atomic deposition in a Co–Al system was investigated using coaxial impact collision ion scattering spectroscopy (CAICISS). Half monolayer of Al and Co atoms were deposited on Co(0001) and Al(001) single crystal surfaces, respectively, in an ultrahigh-vacuum environment. CAICISS analysis of the deposited surface revealed an asymmetric interfacial reaction, as predicted by previous molecular dynamics simulations. Al atoms deposited on a Co substrate are placed on the surface with no interatomic intermixing. In contrast, significant surface intermixing with the deposited Co atoms occurs on the Al(001) substrate, resulting in the formation of a CoAl intermetallic surface layer of B2 structure. These asymmetric features would be important to the understanding of the structural evolution of thin film multilayers. [ABSTRACT FROM AUTHOR]

All three scattering invariants, isotropic, antisymmetric, and anisotropic, contribute to the resonance Raman (RR) activity of randomly oriented gas phase scatterers as shown in a sum-over-all-rovibronic-states approach regardless of the symmetry of the vibrational transition. Thus, in the gas phase, totally symmetric modes may have Raman depolarization ratios (ρ)>3/4 and nontotally symmetric modes may have ρ≠3/4 for resonance excitation frequencies. Large ρ dispersion effects are predicted when the RR scattering cross section is dominated by the contribution of a single vibronic band. The extent of this purely rotational effect sensitively depends on the excitation frequency and the resonant dephasing rate. These depolarization ratio effects are demonstrated by the resonance Raman scattering of CH3I (B state) and NH3, ND3 (A state) for both a and e vibrational bands as well as for J (NH3) and K (CH3I) resolved rovibrational features. [ABSTRACT FROM AUTHOR]

Resonance hyper-Raman (RHR) excitation profiles of rovibrational transitions of NH3 are observed as the incident blue radiation is tuned through two-photon resonance with the v‘2 =2 and v‘2 =3 bands of the UV X→A Rydberg transition. The excitation frequency dependence of the rotationally resolved HREPs are fit by our previously derived intensity expressions [L. D. Ziegler et al., J. Chem. Phys. 87, 4498 (1987)]. These fits to theory reveal J-dependent photodissociation rates for both vibronic bands on the A state surface that correspond to subpicosecond lifetimes. The rotationally assisted dynamical effects are consistent with the previous results of linear rotational Raman excitation profile studies and with an adiabatic centrifugal mechanism which couples rotational motion with the photodissociative reaction coordinate. [ABSTRACT FROM AUTHOR]

The intensities of vibrational resonance hyper-Raman transitions are developed in the usual framework of vibronic theory. In analogy to linear Raman scattering, the leading terms of RHR scattering, A, B, and C, are found when the electronic transitions moments, appearing in the transition hyperpolarizability, are expanded to first order in nuclear coordinate dependence. Noncentrosymmetric molecules are predicted to be the strongest nonlinear scatterers and derive activity from the RHR A term. In contrast to the vibronic analysis of linear Raman scattering, both one and two-photon allowed transitions contribute to RHR scattering cross section at the same order of vibronic theory (B term) for centrosymmetric molecules. RHR scattering spectra of gas phase CH3I, NH3, and CS2 illustrate A- and B-term RHR activity. [ABSTRACT FROM AUTHOR]

Resonance rotational hyper-Raman scattering cross sections excited by identical linearly polarized incident photons are derived for symmetric tops. In the absence of pure dephasing, the rotational structure of a RHR vibrational transition is described, in general, by five scattering invariants which are derived in an irreducible tensor framework. The pattern of relative rotational RHR intensities is a sensitive function of the two-photon resonant vibronic state dephasing constant. High quality rotational RHR spectra of NH3 are obtained using blue incident radiation at half the X→A transition energy. Fits to the observed patterns of relative rotational RHR intensities determine lifetimes of 38, 60, and 100 fs for the v′2 =1,2,3 A state vibronic bands respectively. Although seven rotational branches (N,O,P,Q,R,S,T) are possible in HR, only three (P,Q,R) are observed in these RHR spectra of ammonia due to the magnitude and relative signs of vibronic matrix elements in the scattering cross section expressions. [ABSTRACT FROM AUTHOR]