Postionization fragmentation of rare-gas trimers revisited with new theoretical approaches

Abstract

A new theoretical approach is presented for the general treatment of nonadiabatic hybrid dynamics (mixing classical and quantum approach) and applied to the postionization of rare-gas trimers. There was an important disagreement between trajectory surface hopping (TSH) or mean field (MF) approaches and the experimental results; noteworthy, with the new method qualitative and almost quantitative agreement is found for the fragmentation ratios of ionic monomers and dimers. For the first time in the theory as in the experiment, the dimers prevail for argon while monomers strongly dominate for the heavier rare gases, krypton and xenon. A new compromise between MF and TSH approaches is proposed and the new method is found quite robust with results not too sensitive to various possible implementations.

Photodissociation dynamics of ionic argon pentamer

“…24, the inclusion of quantum decoherence in the MF model leads to a substantial improvement of our theoretical data on the post-ionization fragmentation of rare-gas trimers. We denoted this improved dynamical model as MFQ (Mean-Field with Quenchings) and developed several semi-empirical schemes for the inclusion of quantum decoherence to the original MF method.…”

“…In accordance with our previous studies, we denote this dynamical model as MF (Mean-Field) throughout this work. Very recently [24], we extended the MF model by including quantum decoherence via periodically collapsing the electronic wavefunction to one of the adiabatic electronic states available within the diatomics-in-molecules model.…”

“…Concerning the second step, b, the nuclear velocities are adjusted either via scaling by a scalar factor, the S method of Ref. 24, by adding a vector parallel to the real part of the non-adiabatic coupling vector as proposed originally by Tully [23], method C, or adding a vector parallel to the gradient of the difference of adiabatic electronic energies corresponding to the states the system jumps from and to [33], respectively, method G. The two methods for calculating the collapse probabilities, step a, and the three methods for the after-collapse adjustment of nuclear velocities, step b, give rise to six different schemes for the inclusion of quantum decoherence processes at the MFQ level (see Ref. 24 for details).…”

“…In the AMP method of ref. 24, the collapse probabilities are obtained from electronic wavefunction amplitudes calculated for the current (nuclear configuration dependent) adiabatic basis set; in the TFS method, the Tully's fewest switches algorithm [23] is used for this purpose. Concerning the second step, b, the nuclear velocities are adjusted either via scaling by a scalar factor, the S method of Ref.…”

“…Since a specific adiabatic state is followed at any time, there are no fractionally charged fragments, but the non-adiabatic couplings must be evaluated on the fly, in addition to the electronic Hamiltonian. We have recently proposed a novel method which combines mean-field and trajectory surface-hopping approaches and periodically introduces decoherence [24]. The application of this novel method to the photodissociation of Ar + 5 , for which detailed experimental results are available, is an additional motivation to perform this study.…”