Stepwise formation of H3O(+)(H2O)n in an ion drift tube: Empirical effective temperature of association/dissociation reaction equilibrium in an electric field.
We measured equilibrium constants for H3O(+)(H2O)n-1 + H2O↔H3O(+)(H2O)n (n = 4-9) reactions taking place in an ion drift tube with various applied electric fields at gas temperatures of 238-330 K. The zero-field reaction equilibrium constants were determined by extrapolation of those obtained at non-zero electric fields. From the zero-field reaction equilibrium constants, the standard enthalpy and entropy changes, ΔHn,n-1 (0) and ΔSn,n-1 (0), of stepwise association for n = 4-8 were derived and were in reasonable agreement with those measured in previous studies. We also examined the electric field dependence of the reaction equilibrium constants at non-zero electric fields for n = 4-8. An effective temperature for the reaction equilibrium constants at non-zero electric field was empirically obtained using a parameter describing the electric field dependence of the reaction equilibrium constants. Furthermore, the size dependence of the parameter was thought to reflect the evolution of the hydrogen-bond structure of H3O(+)(H2O)n with the cluster size. The reflection of structural information in the electric field dependence of the reaction equilibria is particularly noteworthy.
Radioactive Isotope Physics Laboratory, RIKEN Nishina Center, Wako, Saitama 351-0198, Japan.
Yoichi
Y
Nakai
Institute of Low Temperature Science, Hokkaido University, Sapporo, Hokkaido 060-0819, Japan.
Hiroshi
H
Hidaka
Institute of Low Temperature Science, Hokkaido University, Sapporo, Hokkaido 060-0819, Japan.
Naoki
N
Watanabe
Atomic Physics Laboratory, RIKEN, Wako, Saitama 351-0198, Japan.
Takao M
TM
Kojima