Photodissociation dynamics of ionic argon pentamer

Photodissociation of the ionized argon pentamer, Ar5+, is studied using an extended diatomics-in-molecules interaction model with the inclusion of the spin-orbit coupling and various dynamical approaches. A thorough comparison with the experimental data available in the literature is presented, including photofragment abundances and their kinetic and internal energy distributions. New predictions are reported for ultraviolet photoexcitation energies, a range that has not been studied before either experimentally or theoretically

Vibrational spectrum of Ar-3(+) and relative importance of linear and perpendicular isomers in its photodissociation

The photodissociation dynamics of the argon ionized trimer Ar 3+ is revisited in the light of recent experimental results of Lepère et al. [J. Chem. Phys. 134, 194301 (2009)], which show that the fragment with little kinetic energy is always a neutral one, thus the available energy is shared by a neutral and ionic fragments as in Ar 2+. We show that these results can be interpreted as the photodissociation of the linear isomer of the system. We perform a 3D quantum computation of the vibrational spectrum of the system and study the relative populations of the linear (trimer-core) and perpendicular (dimer-core) isomers. We then show that the charge initially located on the central atom in the ground electronic state of the linear isomer migrates toward the extreme ones in the photoexcitation process such that photodissociation of the linear isomer produces a neutral central atom at rest in agreement with measured product state distributions

Photoabsorption spectrum of helium trimer cation-Theoretical modeling

The photoabsorption spectrum of He+3 is calculated for two semiempirical models of intracluster interactions and compared with available experimental data reported in the middle UV range [H. Haberland and B. von Issendorff, J. Chem. Phys.102, 8773 (1995)]. Nuclear delocalization effects are investigated via several approaches comprising quantum samplings using either exact or approximate (harmonic) nuclear wavefunctions, as well as classical samplings based on the Monte Carlo methodology. Good agreement with the experiment is achieved for the model by Knowles et al. , [Mol. Phys.85, 243 (1995); Knowles et al. , Mol. Phys.87, 827 (1996)] whereas the model by Calvo et al. , [J. Chem. Phys.135, 124308 (2011)] exhibits non-negligible deviations from the experiment. Predictions of far UV absorption spectrum of He+3 , for which no experimental data are presently available, are reported for both models and compared to each other as well as to the photoabsorption spectrum of He+2 . A simple semiempirical point-charge approximation for calculating transition probabilities is shown to perform well for He+3 .Web of Science13920art. no. 20431

Thermodynamics of small mercury clusters and the role of electronically excited states: a case study on Hg-13

Classical Monte Carlo simulations in the isothermal-isobaric ensemble have been performed for the Hg-13 cluster with the main emphasis paid to structural changes in this cluster induced by elevated temperature and pressure. Broad ranges of temperatures and pressures have been considered so that a comprehensive picture of the structural changes in Hg-13 could be obtained and represented in the form of a phase diagram constructed in the temperature-pressure plane. The effect of the complex electronic structure of the cluster on its electronic ground state potential energy surface and equilibrium thermodynamics has been studied within a semi-empirical electronic structure model based on the diatomics-in-molecules approach. The involvement of (three) lowest excited electronic states has been revealed while the higher excited states available within this model do not contribute.Web of Science24116925691

Two-dimensional multiple-histogram method applied to isothermal-isobaric Monte Carlo simulations of molecular clusters

A two-dimensional multiple-histogram method for isothermal–isobaric ensemble is discussed in detail, implemented for isothermal–isobaric Monte Carlo simulations of molecular clusters, and employed in a case study on phase changes in pure water clusters containing 15 through 21 water molecules. Full phase diagrams of these clusters are reported in the temperature–pressure plane over a broad range of temperatures (T=30–800T=30–800 K) and pressures P=103–109P=103–109 Pa. The main focus of the work is on the structural transformation occurring in the solid phase of these clusters and leading from cluster structures with all molecules on the cluster surface to cage-like structures with one molecule inside, and on how the transformation is influenced by increased pressure and temperature.Web of Science18561605159

Phase transitions in free water nanoparticles. Theoretical modeling of [H2O](48) and [H2O](118)

Classical parallel-tempering Monte Carlo simulations of [H2O]48 and [H2O]118 have been performed in the isothermal–isobaric ensemble and a two-dimensional multiple-histogram method has been used to calculate the heat capacity of the two clusters. A semiempirical procedure is proposed for the inclusion of quantum effects and transformed heat capacity profiles are compared with state-of-the-art experimental data [C. Hock et al., Phys. Rev. Lett., 2009, 103, 073401]. A very good agreement is achieved. A detailed analysis of the simulation data is provided to gain an insight into the nature of the phase change which takes place in the two clusters at T ≈ 100 K.Web of Science1716105371053

Theoretical modeling of ionization energies of argon clusters: Nuclear delocalization effects

Temperature dependence of vertical ionization energies is modeled for small argon clusters (N ⩽ 13) using classical parallel-tempering Monte Carlo methods and extended interaction models based on the diatomics-in-molecules approach. Quantum effects at the zero temperature are also discussed in terms of zero-point nuclear vibrations, either at the harmonic approximation level or at the fully anharmonic level using the diffusion Monte Carlo calculations. Both approaches lead to a considerable improvement of the theoretical predictions of argon clusters ionization energies and represent a realistic way of modeling of ionization energies for weakly bound and floppy complexes in general. A thorough comparison with a recent electron-impact experiment [O. Echt et al., J. Chem. Phys. 123, 084313 (2005)] is presented and a novel interpretation of the experimental data is proposed

Photodissociation dynamics of rare-gas ionic trimers

International audienceSemiclassical mean-field dynamics approach is used in combination with diatomics-in-molecules methods to study photodissociation of ionized trimers of argon, krypton, and xenon. The dynamics of photodissociation is analyzed in terms of the kinetic energy distribution of ionic and neutral fragments, fragmentation patterns, and fragmentation times. Particular attention is paid to the effect of the spin-orbit coupling and clusters temperature. Theoretical results are thoroughly compared with recent experimental as well as theoretical data

Diatomics-in-molecules study of the geometric and electronic structure of Xe-n(+) clusters

Dissociation energies as well as electronic and geometric structure of singly charged xenon cluster cations, Xen+ (n=3–35), are calculated using the extended diatomics-in-molecules method (including the spin–orbit coupling and the most important ionic and neutral three-body interactions) and the state-of-the-art ab initio diatomic curves for Xe2+ due to Paidarová and Gadéa [Chem. Phys. 274 (2001) 1]. Cluster growth of Xen+ and size dependence of the positive charge delocalization are discussed. The calculated dissociation energies are used to estimate the evaporation energies for Xen+→Xen−1++Xe and to study the stability of the Xen+ clusters. The results obtained are compared with available experimental and theoretical data

Thermodynamics of water clusters under high pressures. A case study for (H2O)(15) and (H2O)(15)CH4

Thermal properties and structures of the water cluster containing fifteen molecules, either pure or doped with methane, are studied via classical parallel tempering Monte Carlo calculations in the isothermal–isobaric ensemble. The main emphasis is on structural transformations the cluster undergoes with increasing temperature and pressure. A simple TIP4P interaction model is employed for water and the unified-atom approximation with a Lennard-Jones potential is used to model the methane–water interaction. The results are compared with the data obtained recently for zero temperature via evolutionary algorithm calculations [Hartke, J. Chem. Phys., 2009, 130 art. no. 024905].Web of Science1444155191550