The heat of dissociation of H5+ derived from measurements of ion mobilities

Abstract

The mobility of hydrogen ions in hydrogen at 240, 274, and 295 K has been measured over the E/N range 0.5–10 Td and at gas number densities in the range 8×1016–5×1018 cm−3 using a variable length drift tube of the four gauze type. The absolute error and statistical scatter in the mobility values are estimated to be <±0.5% and <±0.15%, respectively. The equilibrium constant for the reactions H3++H2+H2⇄H5++H2 was obtained by fitting to the variation of the measured mobility with gas number density at low E/N values. Checks were made to ensure the reactions were in equilibrium in the drift space. The derived equilibrium constants and the heat of dissociation 250 meV were found to agree with those of Elford and Milloy and to disagree with those of previous workers. Possible causes for the disagreement are discussed. The zero field reduced mobility of a number of impurity ions in H2 at 293 K was measured. The values were as follows (in cm2 s−1 V−1), CH5+ (11.8±0.1), H3O+ (10.5±0.1), N2H+ (12.1±0.1), and H5O2+ (11.0±0.1).

Toward a realistic density functional theory potential energy surface for the H5+ cluster

“…In Table V we present the calculated values of the present study and compared them with the ones from previous theoretical calculations, [14][15][16]18,20,21,23,27 as well as various experimental measurements. [28][29][30][31]33,[37][38][39] As we can see in Table V the predicted D e and D 0 energies computed here by the DFT calculations are varied from 13.30 and 11.03 kcal/mol using the BLYP to 9.47 and 6.79 kcal/mol with the B3͑H͒ functional, respectively. The results obtained by B3͑H͒ are in fairly good agreement with those obtained by CC studies.…”

“…perature of 25-300 K. [28][29][30][31]33,[37][38][39] The enthalpy variation values are temperature dependent, and generally increase as temperature increases. Therefore, for a direct comparison with the most recent experimental data ͑see van't Hoff plots in Refs.…”

“…However, apart from theoretical predictions on its structure and energetics, the present experimentally confirmed knowledge of the ion is still rather limited. The available molecular spectra, 32,34 which consist of broad rotationally unresolved bands, only provide few vibrational frequencies of H 2 and H 3 + stretching modes, while various experimental [28][29][30][31][37][38][39] data are available for dissociation enthalpies and entropies for the H 3 + +H 2 → H 5 + clustering reaction. More recently, new experimental infrared photodissociation spectra have also reported.…”

Mobilities of Aromatic Ions Drifting in Helium

“…The mobility of ions in a drift field has been an important area of research for many years, 1,2 both from a fundamental interest to probe the interaction between ions and neutral atoms or molecules [3][4][5] and from an applied point of view for modeling the kinetics, dynamics, and energetics of reactions in electric discharges, 6 plasmas, 7,8 and the upper atmosphere. 9 Correlation of ion mobility with structure has been an important new area of interest in mobility studies in recent years.…”

“…The mobility of ions in a drift field has been an important area of research for many years, , both from a fundamental interest to probe the interaction between ions and neutral atoms or molecules − and from an applied point of view for modeling the kinetics, dynamics, and energetics of reactions in electric discharges, plasmas, , and the upper atmosphere . Correlation of ion mobility with structure has been an important new area of interest in mobility studies in recent years. − Experiments have been carried out on carbon clusters C n + ( n < 84), − and a correspondence has been observed between the structures of the cluster ions (linear chains, rings, and three-dimensional spheres) and their mobilities.…”