G. Delgado-Barrio

Photofragmentation of the Ne⋯ICl complex: A three-dimensional quantum mechanical study

Converged three‐dimensional quantum mechanical calculations for photofragmentation of the Ne⋅⋅ICl van der Waals molecule in the energy region of the electronically excited B(3∏0+) state of ICl are presented and compared with experiments. Lifetimes and final state distributions for the ICl fragments were determined for vibrational predissociation from the lowest van der Waals level in the B(v’=2) channel. Good agreement between theory and experiment was achieved using a sum of atom–atom pairwise potentials. This potential energy surface predicts the equilibrium geometry of the complex to be bent at 140° with the Ne atom towards the Cl end of ICl. The diabatic vibrational golden rule (DVGR) approximation, as well as the rotational infinite order sudden approximation (RIOSA), have been tested again the full 3D calculations. Analysis of the quasibound wave function reveals that the highly inverted rotational distribution of the ICl fragments observed in the experiment, is not due to zero‐point bending motion....

ENERGY LEVELS AND STRUCTURE OF TETRA-ATOMIC VAN DER WAALS CLUSTERS

A variational treatment is presented to study bound and quasibound states of X1...BC...X2 van der Waals clusters, where X1 and X2 are rare gas atoms and BC is a conventional diatomic molecule. The Hamiltonian operator, including all the degrees of freedom, is expressed in terms of the B–C relative vector and bond coordinates which describe the position of each rare gas atom with respect to the BC center of mass. In a body‐fixed reference system, with the Z axis parallel to the diatomic axis, all the matrix elements of the Hamiltonian are evaluated in a basis set of functions which takes into account the symmetries of the system. Numerical applications to the He2...Cl2 and Ne2...I2 complexes are presented and discussed.

Three‐dimensional vibrational predissociation of the van der Waals complex He⋅⋅⋅I2(B). A quasiclassical study

We apply a quasiclassical trajectory method to treat vibrational predissociation of the van der Waals molecule He⋅⋅⋅I2(B 3Π). In order to compare with quantum mechanical calculations and the experimental data, we have introduced the rotational degree of freedom by using an approximate treatment. The potential energy surface used was a sum of pairwise atom–atom potentials. The initial conditions were selected at random taking into account previous quantal results. The final rotational distribution for the I2 fragment and the total rate for vibrational predissociation, as functions of vibrational excitation, are in good agreement with the quantum mechanical values and with the experimental measurements.

Comparative configurational study for He, Ne, and Ar trimers

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 Ar3 and Ne3 clusters. Special emphasis is made on the study of the possible Efimov behavior of the first excited state found in the 4He3 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.

A wave packet Golden Rule treatment of vibrational predissociation

The time‐dependent wave packet technique is applied to the Golden Rule treatment of vibrational predissociation. The wave packet at time zero is taken as the product of the quasibound wave function and the coupling inducing predissociation. The rate for vibrational predissociation can then be obtained by Fourier transform into the energy domain of the time‐dependent wave packet autocorrelation function. The method has been applied to a model triatomic van der Waals molecule. It is shown that when the bound‐state components of the wave packet are projected out, the time‐dependent version of the Golden Rule approximation provides an alternative efficient technique to treat intramolecular decay.

Ab initio ground state potential energy surfaces for Rg–Br2(Rg=He, Ne, Ar) complexes

High-level ab initio molecular electronic structure calculations are performed for Rg–Br2 (Rg=He, Ne, Ar) complexes at CCSD(T) (coupled cluster using single and double excitations with a noniterative perturbation treatment of triple excitations) level of theory. Specific augmented correlation consistent basis sets are used for each noble atom (Rg), supplemented with an additional set of bond functions. Effective-core potentials (ECPs), augmented with diffusion (sp) and polarization (3df ) functions, have been employed for the bromine atoms. For all complexes, the CCSD(T) potential energy surfaces (PESs) show double-minimum topology, with wells at both linear and T-shaped configurations; the linear minimum is found to be deeper than the T-shaped one. Vibrational corrections are taken into account for all the complexes and their effects in the stability of the linear and T-shaped conformers are examined. For each complex and each configuration (linear and T-shaped), Re equilibrium intermolecular distances, ...

Vibrational predissociation dynamics of the He79Br2 van der Waals molecule: A quantum mechanical study

The vibrational predissociation of the HeBr2 van der Waals complex is studied by means of both accurate and approximate three dimensional quantum mechanical calculations. Simple atom–atom potentials have been tested for matching experimental measurements at low Br2 vibrational excitations. The fragmentation dynamics when the bromine subunit is close to its B state dissociation limit is then explored and compared with experiments. For low to intermediate vibrational states v, good agreement with most of the data (spectral shifts, lifetimes, average structures, average product energies) is achieved. The closing of the Δv=−1 channel at v=44 and the binding energy at that position are successfully reproduced, although calculated and experimental blueshifts and linewidths are not in such good accordance in the v≳38 range. For these high v excitations, fragmentation cross sections exhibit complicated structures indicating strong interactions among different quasibound states. In addition, interesting threshold ...

The van der Waals potential energy surfaces and structures of He–ICl and Ne–ICl clusters

The potential energy surfaces of the ground electronic state of rare gas interhalogen van der Waals molecules, Rg–ICl (Rg=He, Ne), are calculated at CCSD(T) (coupled cluster using single and double excitations with a noniterative perturbation treatment of triple excitations) level of theory. Calculations have been performed with specific augmented correlation consistent basis sets for the noble atom (Rg), supplemented with an additional set of bond functions. For iodine atom a correlation consistent triple zeta valence basis set in conjunction with large-core Stuttgart–Dresden–Bonn relativistic pseudopotential has been employed. The CCSD(T) results predict the existence of three minima on the Rg–ICl potential energy surfaces at collinear (Rg–ICl), antilinear (Rg–ClI), and near T-shaped configurations, with the collinear structure to be the lowest one. Bound states calculated from the intermolecular potential surfaces show that zero-order vibrational corrections do not alter the stability of the three stru...

Quasiclassical dynamics of the I2–Ne2 vibrational predissociation: A comparison with experiment

The vibrational predissociation dynamics of the I2(B,v)–Ne2 complex is investigated for several vibrational levels of I2, using a quasiclassical trajectory approach. The time evolution of the population of nascent I2 fragments is calculated. A model is proposed which reproduces the results of the classical trajectories, and allows to obtain the lifetimes associated with the dissociation of the two van der Waals (vdW) bonds. The classical lifetimes are higher in general than the experimental ones of Zewail and co‐workers [J. Chem. Phys. 97, 8048 (1992)]. The classical method appears to overestimate mechanisms of energy redistribution between the modes, which slow down the dissociation of the cluster. However, the behavior of the lifetimes with the initial iodine vibrational excitation is in very good agreement with experiment. A sequential path of fragmentation of the two weak bonds via direct predissociation is found to dominate, producing I2(B,v–2)+2Ne fragments. Although with smaller probability, altern...

A new accurate and full dimensional potential energy surface of H5+ based on a triatomics-in-molecules analytic functional form

In this work a reliable full nine-dimensional potential energy surface for studying the dynamics of H(5)(+) is constructed, which is completely symmetric under any permutation of the nuclei. For this purpose, we develop a triatoms-in-molecules method as an extension of the more common diatoms-in-molecules one, which allows a very accurate description of the asymptotic regions by including correctly the charge-induced dipole and quadrupole interactions. Moreover, this treatment provides a semiquantitative description of all the topological features of the global potential compared with coupled cluster results. In particular, the hop of the proton between two H(2) fragments produces a double well in the potential. This resonant structure involving the five atoms produces a stabilization, lowering the barrier, and the triatoms-in-molecules yields to a barrier significantly higher than the ab initio results. Therefore, to improve the triatomics-in-molecules potential surface, two five-body terms are added, which are fitted to more than 110,000 coupled-cluster ab initio points. The global potential energy surface thus obtained in this work has an overall root mean square error of 0.079 kcal/mol for energies below 27 kcal/mol above the global well. The features of the potential are described and compared with previous available surfaces.