José Campos-Martínez

Long‐range interaction for dimers of atmospheric interest: dispersion, induction and electrostatic contributions for O2O2, N2N2 and O2N2

Electric multipole moments, static dipole polarizabilities, and dynamic dipole, quadrupole, and mixed dipole‐octupole polarizabilities of molecular oxygen and nitrogen in their ground electronic states have been obtained by means of high level multiconfigurational ab initio calculations. From these properties, we have obtained electrostatic, dispersion, and induction coefficients for the long‐range interactions of the O2O2, N2N2, and O2N2 dimers. Our data is a comprehensive and consistent set that for N2N2 shows a very good agreement with previous accurate calculations, whereas for quantities involving open‐shell O2 represents a considerable improvement over previous estimations. Moreover, the long‐range interaction is analyzed and compared for the different interacting partners. It is found that the C8 dispersion interaction plays a nonnegligible role and that the induction component is only important for a detailed description of the highest order anisotropy terms in the spherical harmonics expansion of the long‐range potential. It is also found that the total long‐range interaction is quite similar in O2O2 and O2N2, and that differences with N2N2 are mainly because of the important role of the electrostatic interaction in that dimer. Comparison with high level supermolecular calculations indicates that the present long‐range potentials are accurate for intermolecular distances larger than about 15 bohr.

Wave packet study of the Ne2I2 fragmentation dynamics: a four degrees of freedom model

Abstract We present a four degrees of freedom model that accounts for all possible fragmentation mechanisms in the vibrational predissociation of the Ne 2 I 2 van der Waals cluster. Calculations are performed by wave packet propagation and results are interpreted in terms of an analytical sequential model leading to a good agreement with experimental data.

Double continuum fragmentation in the vibrational predissociation X⋅⋅⋅BC(v)⋅⋅⋅Y→BC(v’<v)+X+Y of van der Waals complexes: A perturbative treatment

We present an approximate quantal model to study the double continuum problem arising in the complete fragmentation of X⋅⋅⋅BC(v)⋅⋅⋅Y van der Waals(vdW) complexes, where BC is a conventional diatomic molecule vibrationally excited and X and Y are rare gas atoms, through vibrational predissociation (VP). Assuming a near equilibrium geometry of the complex and using an adiabatic approximation for describing the oscillation in the angle formed by the BC⋅⋅⋅X and BC⋅⋅⋅Y weak bonds, the rates for complete fragmentation are expressed in the frame of Fermi’s ‘‘Golden Rule’’. Double continuum wave functions may be obtained by a perturbative treatment that allows one to take properly into account the symmetry of the problem in the particular and very frequent case X≡Y.

Time-dependent Hartree study of lifetimes for the Ne2I2 van der Waals cluster

Abstract The vibrational predissociation of the Ne2I2 van der Waals cluster is studied by a time-dependent Hartree type approach. Lifetimes for different initial vibrational states of I2 are computed and compared with the experimental results. The validity of this approach for studying vibrational predissociation is explored as well as the limitations and advantages.

A time-dependent wave packet approach for reaction and dissociation in H2 + H2

Abstract A time-dependent wave packet method to study four center (4C) reactions in competition with collision-induced dissociation is presented and applied to the H 2 +H 2 system, using the potential of Aguado et al. [J. Chem. Phys. 101 (1994) 4004] and a reduced dimensionality model. The calculated probabilities are better converged than previous time-independent quantum calculations and, in addition, compare quite satisfactorily with quasiclassical trajectory calculations. Tunneling effects near reaction thresholds are, however, important. For the 4C reaction in H 2 ( v 1 =10)+H 2 ( v 2 =0), it is estimated that such effects are dominant for temperatures below 1200 K, with decreasing values for more excited initial states or for the dissociation process.

Quasiclassical trajectory study of reactive and dissociative processes in H2+H2: Comparison with quantum-mechanical calculations

Quasiclassical trajectory calculations have been carried out for H(2)(v(1)=high)+H(2)(v(2)=low) collisions within a three degrees of freedom model where five different geometries of the colliding complex were considered. Within this approach, probabilities for different competitive processes are studied: four center reaction, collision induced dissociation, reactive dissociation, and three-body complex formation. The purpose is to compare in detail with equivalent quantum-mechanical wave packet calculations [Bartolomei et al., J. Chem. Phys 122, 064305 (2005)], especially the behavior of the probabilities near reaction thresholds. Quasiclassical calculations compare quite well with the quantum-mechanical ones for collision induced dissociation as well as for the four center reaction, although quantum effects become very important near thresholds, particularly for lower v(1)s and for the four center process. Less quantitative agreement is found for reactive dissociation and three-body complex formation. It is found that most quantum effects are due to differences between quantum and classical vibrational distributions of H(2)(v(1)=high). Zero point energy violation has been found in the classical reactive-dissociative probabilities. Extension of these findings to full-dimensional treatments is examined.

Anharmonicity effects on the vibrational predissociation of the NeI2(B 3Πu+, ν) complex: A close-coupling infinite-order sudden treatment

Abstract A model previously applied to study the vibrational predissociation (VP) of HeI2(B, ν) is extended to treat the VP of NeI2(B, ν) in the region of initial vibrational excitation 28⩽ν⩽34. Due to the anharmonicity of the diatomic subunit, the usually predominant channel for VP, Δν=−1, becomes energetically forbidden. This gives rise to oscillations of the VP rate as a function of ν that no longer follows the typical superlinear behaviour shown in the low diatomic excitation regime.

Study of the electronic‐to‐vibrational energy transfer in the quenching process of Na*(3 2P) with N2(1Σ+g,v=0). A quantal close coupling calculation

Electronic‐to‐vibrational energy transfer has been studied by solving numerically the close‐coupling equations, in the T‐shape configuration, on the two lowest electronic states of the Na–N2 system. The diabatic potential surfaces were taken from Archirel and Habitz while the interelectronic coupling was modeled by different Gaussian‐type functions. Different sets of parameters for the coupling were used in order to study the final vibrational distributions of N2. Finally, partial quenching probabilities are presented and compared with previous theoretical and experimental works.

Comparative investigation of pure and mixed rare gas atoms on coronene molecules

Clusters formed by the combination of rare gas (RG) atoms of He, Ne, Ar, and Kr on coronene have been investigated by means of a basin-hopping algorithm and path integral Monte Carlo calculations at T = 2 K. Energies and geometries have been obtained and the role played by the specific RG-RG and RG-coronene interactions on the final results is analysed in detail. Signatures of diffuse behavior of the He atoms on the surface of the coronene are in contrast with the localization of the heavier species, Ar and Kr. The observed coexistence of various geometries for Ne suggests the motion of the RG atoms on the multi-well potential energy surface landscape offered by the coronene. Therefore, the investigation of different clusters enables a comparative analysis of localized versus non-localized features. Mixed Ar-He-coronene clusters have also been considered and the competition of the RG atoms to occupy the docking sites on the molecule is discussed. All the obtained information is crucial to assess the behavior of coronene, a prototypical polycyclic aromatic hydrocarbon clustering with RG atoms at a temperature close to that of interstellar medium, which arises from the critical balance of the interactions involved.

Energy levels and dynamics of vibrational predissociation of NeCl2: Approximate quantum mechanical calculations.

Abstract Metastable energy levels and rates for vibrational predissociation of NeCl2 (B, v1 = 11) complex are investigated. The potential energy surface is represented by the sum of atom-atom pairwise interactions. Due to the large vibrational spacing of Cl2 (B), a diabatic distorted-wave approximation is used to describe diatomic vibrations. Discrete energy levels are then calculated by separating adiabatically the fast stretching motion in the weak bond from the slow rotational motions within the complex. Continuum states are described in the “infinite order sudden” (I.O.S.) approximation, and rates for vibrational predissociation are evaluated using the corresponding discrete-continuum potential couplings in the frame of the Fermis golden rule.