The dissociative recombination rate coefficients of H+3, HN+2, and HCO+

Abstract

The dissociative recombination rate coefficients for H+3, HN+2, and HCO+ are determined at 110, 210, and 273 K by monitoring the decay of the infrared absorption signals as a function of time. The rate coefficients are 1.8, 7.0, and 3.1 in units of 10−7 cm3 s−1 for H+3, HN+2, and HCO+, respectively, at 273 K. These values agree very well with those obtained using the stationary afterglow or the merged beam techniques, but the values for H+3 disagree with that obtained by Smith and co-workers (≤2×10−8 cm3 s−1) using the flowing afterglow/Langmuir probe method. The rate coefficients for H+3 and HCO+ disagree with theory which has predicted very slow dissociative recombinations in the lower vibrational states. The temperature dependences obtained here, although the temperature range is rather limited, are consistent with those obtained previously using the stationary afterglow (for H+3 and HCO+) and the merged beam (for HN+2) techniques. The measurements are extended to several vibration–rotation levels and no significant rotation dependence of the rate coefficients is observed. It has also been found that the ions investigated here can be equally abundant at ice temperature as at liquid nitrogen temperature.

Deuterium chemistry in the Orion Bar PDR

“…The new model takes into account the new branching ratios of the N 2 H + dissociative recombination (Molek et al 2007), and computes the pre-exponential factors of the reverse reactions involved in the deuterium fractionation of CH + 3 with the proper factors involved in the translational partition functions. In addition, we have included the branching ratios of the electronic recombination of HCO + from Amano (1990), where the channel towards CO is found to be predominant. The radiative association reactions of CH + 3 and deuterated substitutes with H 2 have been derived from the theoretical predictions of Bacchus-Montabonel et al (2000), who provide values for different temperatures.…”

Kinetic processes in recombining H 3 + plasmas

“…If one is unaware of this, one may conclude that one observes binary, rather than ternary recombination. Bates et al [12] pointed this out in their famous 'enigma' paper while trying to explain the experimental observations in H + 3 afterglows of Amano [5]. The collisional part of CRR (the first term in equation (2.1)), when written as A + + 2e − → A(n, l) + e − , looks like the inverse of electron-impact ionization, but the highly excited product neutrals (with principal and angular momentum quantum numbers n and l) are quickly re-ionized and enter an approximate Saha equilibrium with the free electrons.…”

“…Afterglow plasmas at higher densities, however, explore additional mechanisms to return to the neutral state, as is immediately apparent when one examines historical recombination data. Figure 1 compares selected afterglow rate coefficients [2,3,5,6] to the thermal recombination coefficient inferred from earlier ISR experiments [4].…”

“…This brief contribution adds some ideas on the interpretation of afterglow data, and proposed three-body 10 -6 Macdonald et al [2] Glosík et al [3] McCall et al [4] Amano [5] Leu et al [6] 10 -7…”

Simplified model to describe the dissociative recombination of linear polyatomic ions of astrophysical interest

“…However, the available literature on the DR of this molecular ion is scarce and, from the theoretical point of view, somehow incomplete. Several experiments on DR in N 2 H + have been made [21][22][23] producing somewhat different rate coefficients as shown on the right panel of Fig. 4.…”