Use of correlated potential harmonic basis functions for the description of the 4He trimer and small clusters J. Chem. Phys. 134, 164106 (2011); 10.1063/1.3583365Bound-state energies in argon trimers via a variational expansion: The effects from many-body corrections Helium trimer bound states are calculated by means of a variational method described in terms of atom pair coordinates and distributed Gaussian basis functions for zero total angular momentum. To show the feasibility of this method, we also apply it to the calculation of the first vibrational levels of the Ar 3 and Ne 3 clusters. Special emphasis is made on the study of the possible Efimov behavior of the first excited state found in the 4 He 3 trimer. Geometrical configurations of the ground and first excited states of these rare gas trimers have been exhaustively studied owing to the proper symmetry of the coordinates chosen.

The dynamics of polarized fluorescence in reduced nicotinamide adenine dinucleotide (NADH) at 460 nm under two-photon excitation at 720 nm by femtosecond laser pulses in water−methanol solutions has been studied experimentally and theoretically as a function of methanol concentration. A number of fluorescence parameters have been determined from experiment by means of the global fit procedure and then compared with the results reported by other authors. A comprehensive analysis of experimental errors was made. Ab initio calculations of the structure of NADH in water and methanol and of β-nicotinamide mononucleotide (NMNH) in vacuum have been carried out for clarifying the role of decay time heterogeneity. The main results obtained are as follows. An explanation of the heterogeneity in the measured fluorescence decay times in NADH has been suggested based on the influence of the internal molecular electric field in the nicotinamide ring on nonradiative decay rates. We suggest that different charge distributions in the cis and trans configurations result in different internal electrostatic field distributions that lead to the decay time heterogeneity. A slight but noticeable rise of the fluorescence decay times τ 1 and τ 2 with methanol concentration was observed and treated as a minor effect of a nonradiative relaxation slowing due to the decrease in solution polarity. Relative concentrations of the folded and unfolded NADH conformations in solutions have been determined using a new method of analysis of the rotational diffusion time τ r as a function of methanol concentration on the basis of the Stokes−Einstein−Debye equation. The analysis of the fluorescence anisotropy parameters obtained under linearly and circularly polarized excitation and the parameter Ω has been carried out and resulted in the determination of the two-photon excitation tensor components and suggested the existence of two excitation channels with comparable intensities. These were the longitudinal excitation channel dominated by the diagonal tensor component S zz and the mixed excitation channel dominated by the off-diagonal tensor components |S xz 2 + S yz 2 | 1/2 .

Helium trimer bound states are calculated with a variational method described in terms of pair atom coordinates and distributed Gaussian functions by assuming zero total angular momentum. With the two-body interaction potential used, a weakly bound state for the dimer and only two bound states for the trimer are found. Although strictly speaking the first excited trimer state is not an Efimov state, we show that this state presents several characteristics of the Efimov behavior which are extensively discussed in the present work. Special emphasis is placed on the main geometrical configurations contributing to the two bound trimer states, and suggestions are made on the possible ways of experimentally detecting the Efimov-type state. [S0031-9007(99) [4]. A lot of theoretical work concerning these special states has been done in order either to confirm or to disprove their existence [5][6][7][8]. However, much of the controversy about their existence is chiefly due to uncertainties on the two-body (2B) interaction potential and only in part to the different dynamical methods applied.In this Letter, our purpose is twofold. First, to apply a variational method based on pair coordinates leading to a more suitable way to discuss configurations and symmetrization of the ground and excited states of the trimer; and, second, to discuss whether or not Efimov states can be observed. Concerning the first point, it is obvious that even using the same 2B interaction, the theoretical model applied to solve the trimer discrete spectrum can be crucial for bound states very near to the three-body threshold, as is the case for the Efimov states. Moreover, using this kind of coordinate the weight of the different geometrical configurations can be estimated allowing one to know which of them would dominantly contribute to those special states. As far as we know, this is the first "exact" variational calculation including the proper symmetry of the problem. Finally, from our knowledge of the pair distribution function and of the main geometrical configurations, it becomes possible to determine the average size of this floppy system, and therefore to envisage different ways to observe them.Considering a zero total angular momentum state, using atom-atom pair coordinates (R 1 , R 2 , R 3 ) and including a scale factor ͑R 1 R 2 R 3 ͒ 1͞2 to attain the standard normalization in the total wave function, a totally symmetric Hamiltonian is obtainedwith V being the 2B-interaction potential (which corresponds in this work to that of Ref.[9]), and where the effective kinetic energy operators t i are expressed as

The scattering of atomic nitrogen over a N-pre-adsorbed W(100) surface is theoretically described in the case of normal incidence off a single adsorbate. Dynamical reaction mechanisms, in particular Eley-Rideal (ER) abstraction, are scrutinized in the 0.1-3.0 eV collision energy range and the influence of temperature on reactivity is considered between 300  and 1500 K. Dynamics simulations suggest that, though non-activated reaction pathways exist, the abstraction process exhibits a significant collision energy threshold (0.5 eV). Such a feature, which has not been reported so far in the literature, is the consequence of a repulsive interaction between the impinging and the pre-adsorbed nitrogens along with a strong attraction towards the tungsten atoms. Above threshold, the cross section for ER reaction is found one order of magnitude lower than the one for hot-atoms formation. The abstraction process involves the collision of the impinging atom with the surface prior to reaction but temperature effects, when modeled via a generalized Langevin oscillator model, do not affect significantly reactivity.