P. Mareca

Matrix elements for anharmonic potentials: Application to I2 morse oscillator

Many authors have contributed expressions for obtaining analytical matrix elements for Morse oscillators. In this work, we discuss the advantages of using these expressions. At the same time, we propose a full numerical method to calculate these matrix elements and we compare, for the I2 system, the different results given by Gallas, Vasan, and Cross, and the variational method.

A close‐coupling infinite order sudden approximation (IOSA) to study vibrational predissociation of the HeI2 van der Waals molecule

We apply in this paper a model related to the ‘‘infinite order sudden approximation’’ to treat the vibrational predissociation of the HeI2 van der Waals molecule. For each configuration, the stretching motions within the complex are exactly solved in the close‐coupling formalism. The bending motion is then considered in an approximate way and averaged predissociation rates are obtained. Our results are compared with the experiment and also with previous models.

Determination of a potential energy surface for the van der Waals molecules NeI2(B)

Abstract The van der Waals (vdW) interaction Ne… I 2 (B) is assumed to be described by the sum of NeI Morse potentials. By iterative application of an adiabatic rotational model, the relevant parameters D (well depth) and α (inverse characteristic length) are determined in order to fit the available experimental data. The applied procedure is very efficient. The full potential, obtained by adding the I 2 potential to the vdW interaction, is expected to be accurate enough to allow us a realistic study of vibrational predissociation (VP) process of this complex.

Classical trajectory study of tetraatomic van der Waals molecules: complex HeI2Ne

Abstract We are interested in the study of dynamics of van der Waals (vdW) molecules consisting in a diatomic molecule plus two rare gas atoms. In particular, our goal is to elucidate the competitivity between both vdW bonds in a process of vibrational predissociation (VP), i.e., in the transference of vibrational energy stored in the diatomic molecule towards one or another vdW bond, giving eventually rise to its breaking. In this paper, the formalism of classical trajectories within the “infinite order sudden” approximation (I.O.S.A.) is presented for this special four-body problem. Also, preliminary results for HeI 2 Ne in the T-shape configuration, with the rare gas atoms placed at different side of the diatom, are shown and discussed.

Vibrational predissociation of highly vibrationally excited He…I2 VDW molecule. A quasiclassical trajectory calculation.

Abstract We apply a quasiclassical trajectory method to treat vibrational predissociation of the van der Waals molecule He…I 2 (B 3 π) in the range of high initial vibrational excitation of I 2 , 50 ⩽ v 1 ⩽ 63. The vibrational predissociation rates, as a function of v 1 , shows a behaviour in good agreement with the recent experimental data. A peaking of that function is found at v 1 ⋍ 56. The propensity rule of the lost of one vibrational quantum by the I 2 in the process, established in a lower diatomic vibrational excitation range, is broken in the high range studied here. Also, because the small rotation excitation of the I 2 fragment obtained, the He…I 2 vibrational predissociation can be considered as a nearly V-T process.

Theoretical study of neutral and charged Fe7-(C6H6)m, m = 1, 2 rice-ball clusters.

Bonding of benzene molecules on the surface of neutral and charged Fe7 clusters, which have pentagonal bipyramids (PBP), was studied by means of all-electrons density functional calculations. Dispersion corrections were done with the BPW91-D2 method using the 6-311++G(2d,2p) basis sets. With two less coordinated equatorial sites (bonded to four iron atoms) and one axial site (bonded to five atoms), a triangular face of Fe7 emerges as the basic unit for the absorption of benzene moieties. Bonding of benzene (Bz) on such triangle yields the ground state (GS) for Fe7Bz, Fe7Bz(-), and Fe7Bz(+). Without dispersion, in the GS of Fe7Bz(-), the ligand is η(6) coordinated with a single equatorial iron site, and in the GSs of Fe7Bz2 and Fe7Bz2(-), each benzene moiety is η(6) bonded on opposite equatorial sites. However, BPW91-D2 yields GS structures for Fe7Bz2, Fe7Bz2(-), and Fe7Bz2(+), where the absorption is done on opposite triangles. Therefore, dispersion corrections are crucial for a proper study of Fe7Bz2. The multiplicities (M = 2S + 1, where S is the total spin) of these species, 17, 16, and 18, respectively, are smaller than those of Fe7(23), Fe7(-)(22) and Fe7(+)(24) showing important quenching of the magnetic moment of Fe7. Bond dissociation energies (BDE), in kcal/mol, for Fe7Bz (32.7), Fe7Bz(+) (47.3), and Fe7Bz(-) (27.2) show bigger (smaller) values for the cation (anion). A similar picture was found for the BDEs of Fe7Bz2. Ionization energies, 5.37 and 4.94 eV, for m = 1 and 2 are smaller than that of Fe7, 6.00 eV; which is due to delocalization of the electrons through the network of 3d-π bonds. Electron affinities of Fe7Bz1,2 are also smaller than that of Fe7, being mainly due to the increased repulsion.

Applications of an adiabatic rotational model to the Ar…O2 van der Waals molecule

Abstract In this paper a separation of vibrational and rotational motions is applied to describe the metastable levels of the ArO 2 van der Waals molecule. The potential energy surface is written as a sum of atom—atom pairwise Morse functions, the parameters being obtained by fitting the potential of Pirani and Vecchiocattivi at the equilibrium configuration. The results agree fairly well with experimental data about infrared absorption, assuming a J = 2 → 1 transition, where J is the quantum number associated to the total angular momentum of the complex. Also, close coupling three-dimensional calculations about the ArO 2 collision show a good agreement with some energies previously calculated. The widths for rotational predissociation have been estimated by this procedure to be of the order of 1 cm −1 .

Theoretical spectroscopic study of van der Waals systems

Abstract In this paper we discuss the application of three dimensional quantum models, in order to study the dynamics of vibrational predissociation of van der Waals molecules. In the first model the vibrations are described in the distorted-wave diabatic approximation while rotations are treated in the sudden approximation. The second model is related to the “Infinite order sudden approximation” and after a close coupling formalism for the vibrations, the bending motion is considered in an approximate way. We present the 3D quasibound levels and the rates for vibrational predissociation in a test case, the HeI2.

Infrared bound to quasibound spectrum of HeD+: an application of the artificial channel method

Abstract Some energy transitions from bound to rotational quasibound levels of the ground state of HeD + have been calculated within the framework of the “artificial channel” method using an adiabatic potential. Modelling the dipolar moment responsible of the transition, we find a good agreement with previous theoretical calculations and experimental data when high rotational states are involved in the transition. However, for the lower states, the results are very sensitive to the interpolation method used to obtain the necessary fine grid describing the potential curve.

Dynamical problems in van der Waals systems: Application to He I2.

Abstract In this paper we present several theoretical models in order to get a potential surface for triatomic van der Waals complexes. Our purpose is to describe Energy and also time resolved experimental data. In this way, the potential surface for the He…I 2 system is obtained as the sum of three atom-atom Morse functions.