Binary and ternary recombination of para-${\rm H}_3^+$H3+ and ortho-${\rm H}_3^+$H3+ with electrons: State selective study at 77–200 K

Abstract

Measurements in H(3)(+) afterglow plasmas with spectroscopically determined relative abundances of H(3)(+) ions in the para-nuclear and ortho-nuclear spin states provide clear evidence that at low temperatures (77-200 K) para-H(3)(+) ions recombine significantly faster with electrons than ions in the ortho state, in agreement with a recent theoretical prediction. The cavity ring-down absorption spectroscopy used here provides an in situ determination of the para/ortho abundance ratio and yields additional information on the translational and rotational temperatures of the recombining ions. The results show that H(3)(+) recombination with electrons occurs by both binary recombination and third-body (helium) assisted recombination, and that both the two-body and three-body rate coefficients depend on the nuclear spin states. Electron-stabilized (collisional-radiative) recombination appears to make only a small contribution.

Binary recombination of para- and ortho-H 3 + with electrons at low temperatures

“…Because of this agreement at higher temperatures, where CRR is negligible, we conclude that the measured rate coefficients at 77 K do not depend on the electron density. From this, it follows that CRR has little to no effect on the plasma decay and that the obtained recombination rate coefficients p a bin and o a bin correspond to the binary DR (for details see discussion in the study of Dohnal et al [25]). Further results concerning ternary recombination have been published elsewhere [25], together with a detailed discussion of the equilibrium conditions in the recombining afterglow plasma and with an estimation of the effect of the CRR process.…”

“…We have proved experimentally [25,26] that the assumption of TDE under our experimental conditions is correct. To obtain a eff from the measured electron density decay curves, we used direct fits to the data and, in addition, the more advanced 'integral analysis' technique [31].…”

“…The possible effects of another ternary process-collisional radiative recombination (CRR) [23,24]-are discussed in detail elsewhere [25].…”

State selective study of H3+recombination in Cryo-FALP and SA-CRDS experiments at 77 K

“…[8][9][10][11]. The advantage of the afterglow experiments is that H + 3 ions are rotationally thermalized by multiple collisions with ambient neutral gas molecules/atoms at properly chosen conditions [5,12]. In the recent afterglow type experiments the evolution of densities of H + 3 ions in the particular spin state and the thermalisation (rotational temperature within para and ortho nuclear spin manifolds and kinetic temperature) are monitored by a laser absorption spectroscopy (SA-CRDS -Stationary Afterglow with Cavity Ring-Down absorption Spectrometer [6,7,13]).…”

“…[5]. The state-specific binary recombination has been studied by monitoring decay of the low temperature H + 3 dominated afterglow plasma (in He/Ar/H 2 gas mixture) [5][6][7] and also by several storage ring experiments, see Refs. [8][9][10][11].…”