Integral and differential cross section measurements at low collision energies for the N2++CH4/CD4 reactions

Abstract

Absolute integral cross sections are measured in the collision energy range between 0.1 to 3.5 eV for the N2++CH4 and N2++CD4 reactions using the universal guided ion beam apparatus. The reaction branching ratio, CX3+:CX2+:N2X+ (X=H or D), is found to be 0.86:0.09:0.05 and 0.88:0.07:0.05 for the N2++CH4 and N2++CD4 reactions, respectively. The CH3+/CH2+ ratio is constant over the whole collision energy range and very similar to the one obtained for the almost isoenergetic Ar++CH4 reaction. Axial velocity distributions of the product ions are measured by time of flight at collision energies between 0.1 and 3.5 eV. The results provide direct insight into the reaction dynamics. The dissociative charge transfer channels, leading to CH3+ and CH2+ product ions, occur via an electron jump combined with some exchange of momentum between the colliding partners. The H (D) transfer leading to N2H+ can be described as a direct process, similar to a spectator stripping mechanism. Various isotope effects are observed, the dominant being that the cross sections for reaction with CH4 are up to 20% bigger than the corresponding ones for CD4.

CRITICAL REVIEW OF N, N + , N + 2 , N ++ , And N ++ 2 MAIN PRODUCTION PROCESSES AND REACTIONS OF RELEVANCE TO TITAN'S ATMOSPHERE

“…In spite of a slight increase of the rate constant at low temperatures, 1.20 × 10 −9 at 70 K and 1.90 × 10 −9 at 8-15 K, the difference with the value of the rate constant at 300 K is not significant. The rate constant seems effectively unchanged over the temperature range 8-300 K, so the recommended value is the same at 300 K and 150 K. The study of Nicolas et al (2003b) shows, however, a substantial increase of the rate constant with collision energy, and in the thesis report of Nicolas (2002), a variation of less than 20% in the rate constant is observed with vibrational energy (v = 0-4). A small isotopic effect has been observed by Nicolas et al (2003b), who measured, in the 0.1-3 eV E CM range, rate constants equal to (1.53-2.83) × 10 −9 cm 3 s −1…”

“…So the recommended rate formation being the major channel. The nondissociative charge transfer product CH + 4 is not observed (less than 0.2% in the study of Nicolas et al (2003b) because a large amount of internal energy is transferred to the primary CH + 4 product which then dissociates. However, there is an important disagreement concerning the production of N 2 H + .…”

“…However, there is an important disagreement concerning the production of N 2 H + . Only three studies relate its formation (McEwan et al 1998;Nicolas et al 2003b;C. Alcaraz et al, unpublished).…”

“…In conclusion, the product branching ratio of this reaction seems to be constant as a function of temperature and vibrational excitation of N + 2 parent ions within experimental uncertainties. Our recommended yields are the values from Nicolas et al (2003b).…”

Bond-Forming Chemistry in the Gas-Phase Reactions of Atomic and Molecular Dications and Trications

“…However, ingenious use of pulsed reactant beams, coupled with measurements of the TOF of reaction products to the detector, has in fact allowed considerable insights into reaction dynamics to be gleaned from GIB experiments. 64 …”