Dissociative recombination of rotationally coldH3+

Abstract

This paper presents the first dissociative recombination (DR) measurement of electrons with rotationally and vibrationally cold H 3 + ions. A dc discharge pinhole supersonic jet source was developed and characterized using infrared cavity ringdown spectroscopy before installation on the CRYRING ion storage ring for the DR measurements. Rotational state distributions ͑T rot ϳ 30 K͒ produced using the source were comparable to those in the diffuse interstellar medium. Our measurement of the electron energy dependence of the DR cross section showed resonances not clearly seen in experiments using rotationally hot ions, and allowed calculation of the thermal DR rate coefficient for ions at interstellar temperatures, ␣ DR ͑23 K͒ = 2.6ϫ 10 −7 cm 3 s −1 . This value is in general agreement with recent theoretical predictions by Kokoouline and Greene [Phys. Rev. A 68, 012703 (2003)]. The branching fractions of the two breakup channels, H+H+H and H+H 2 , have also been measured for rotationally and vibrationally cold H 3 + .

Water deuterium fractionation in the high-mass star-forming region G34.26+0.15 based on Herschel/HIFI data

“…For the reactions involving these species, we have applied spin selection rules to know which reactions are allowed, and have determined branching ratios assuming a total scrambling and a pure nuclear spin statistical weight. Some of the rate coefficients of these reactions have been theoretically or experimentally determined (Marquette et al 1988;Jensen et al 2000;McCall et al 2004;Dos Santos et al 2007;Hugo et al 2009;Honvault et al 2011a,b;Dislaire et al 2012) and for these we used the calculated or measured values. We have benchmarked our model against some previous work that includes spinstate chemistry, using the same conditions as described in Figure 8 of Pagani et al (2009) and Figure 4 of Sipilä et al (2013): a temperature of ∼10 K and a density from ∼10 5 to ∼10 6 cm −3 .…”

Chemistry, astronomy and physics of H 3 +

“…Both discrepancies among experimental values of the DR rate constants, and those between experiment and theory, have been greatly reduced. The advent of a low-temperature ion source has led to a nearperfect agreement between the experiments by both the CRYRING [20] and the TSR on the energy-dependent resonant structure [21] and the cross section [22].…”

Kinetic processes in recombining H 3 + plasmas

“…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…”