Inverse kinetic isotope effects in the charge transfer reactions of ammonia with rare gas ions

Abstract

In the absence of experimental data, models of complex chemical environments rely on predicted reaction properties. Astrochemistry models, for example, typically adopt variants of capture theory to estimate the reactivity...

Charge Transfer Reactions between Water Isotopologues and Kr+ ions

“…A time delay of ∼15 s is introduced to allow for sympathetic cooling of the Kr + ions into the crystal, and to ensure that all Kr + ions are in the ground electronic state. 8,11 Any Kr + ions produced in the higher energy 2 P 1/2 spin state have a lifetime of only 340 ms, decaying to the ground 2 P 3/2 state via a magnetic-dipole-allowed transition with an Einstein coefficient of A m = 2.8 s −1 . 14 H 2 O or D 2 O vapor at 293 K is admitted to the reaction chamber through a second high-precision leak valve, initiating the charge transfer reactions.…”

“…19,20 As our reactions take place at temperatures around 240 K, ADO is expected to approximately predict the rate of capture. Further details on the ADO calculations are provided in previous work; 7,8 the constants and input parameters used in this work are set out in Table 2. Experimental rate coefficients are set out in Table 1 and Figure 2, alongside the predicted values from the ADO calculations.…”

“…1.8( 7 ground gases in the reaction chamber are removed by a heat exchange device. 7,8 Any remaining species are identified with a residual gas analyzer (RGA). Under the experimental conditions, reactions between Kr + ions and background species present in the reaction chamber are typically absent or negligible.…”

“…Such behavior was observed in the charge transfer of ammonia isotopologues with rare-gas ions (Xe + , Kr + , and Ar + )with the experimental rate coefficients consistently lower than those predicted by capture theory. 7,8 The charge transfer processes also exhibited an unexpected inverse kinetic isotope effect (KIE): for all three rare-gas ions studied, ND 3 reacted faster than NH 3 . Ammonia is known to be present in the ISM, with both ND 3 and NH 3 spectroscopically identified.…”

Rotational Cooling Effect on the Rate Constant in the CH3F + Ca+ Reaction at Low Collision Energies

“…Subsequently, other groups began to measure low-temperature ion–polar-molecule reactions relevant to astrochemisty using Coulomb crystals of ions. − An interesting finding is the different reactivity of para- and ortho-water molecules in the H 2 O + N 2 H + → N 2 + H 3 O + reaction . Kilaj et al performed reaction rate measurements by colliding supersonic H 2 O beams containing rotational state-selected para-H 2 O or ortho-H 2 O with translationally cooled N 2 H + ions.…”