Temperature Measurement from the Translational Kinetic Energy Release Distribution in Cluster Dissociation:  A Theoretical Investigation

Abstract

Unimolecular dissociation of neutral and charged argon clusters is theoretically investigated in the context of calorimetric measurements. The temperature of the product cluster is estimated from the distribution of the translational kinetic energy released (KER), assumed to have the form f(epsilon) approximately epsilon(alpha) exp(-epsilon/k(B)T). Phase space theory (PST) in its orbiting transition state (OTS) version is validated by comparing its predictions to the results of large-scale molecular dynamics simulations. The temperatures estimated from the KER distributions are seen to be generally lower than the actual microcanonical temperature computed from independent Monte Carlo simulations of the product cluster at thermal equilibrium. On the basis of these deviations, the various approximations leading from the rigorous PST/OTS treatment to the assumed exponential form are critically discussed. In the case of Ar(n)(+) clusters, the use of a quantum diatomic-in-molecules Hamiltonian constructed from recent ab initio calculations reveals some possible inadequacies of the 1/r(4) ion/dipole interaction at intermediate distances due to some residual charge transfer.

Evidence for cluster shape effects on the kinetic energy spectrum in thermionic emission

“…Our approach follows similar ideas originally developed for spherical clusters, 7 and consists in calculating a realistic KER distribution based on molecular ingredients, fitting subsequently these spectra to effective exponential forms. Our approach follows similar ideas originally developed for spherical clusters, 7 and consists in calculating a realistic KER distribution based on molecular ingredients, fitting subsequently these spectra to effective exponential forms.…”

A unimolecular evaporation model for simulating argon condensation flows in direct simulation Monte Carlo

“…Note that in Ref. 24 the numerical results based on a phase space theory ͑PST͒ approach suggest a value of ␤ =2/ 3 as a best fit to Eq. ͑6͒.…”

“…23 Since the total energy and mass of the cluster without evaporation are constant, we may describe the cluster as being in an equilibrium state during which the internal kinetic energy and temperature fluctuate frequently. Calvo et al 24 proposed that the distribution of argon atom kinetic energy inside a cluster, e k,i , has the following analytical form:…”

On the accuracy of thermionic electron emission models. I. Electron detachment from SF6−

“…͑3.3͒ is based on experimental data over a range of and E − EA up to about 0.2 eV only, such that differences between the VW and VW+ IVR curves at Ͼ0.2 eV may at least in part be artificial. [30][31][32] The distribution functions f͑E , ͒ of Fig. 3 can be further rationalized by separately inspecting the average energy ͗͘ of the emitted electrons and the shape of the reduced distribution functions f͑E , / ͗͒͘.…”