Dissociative recombination of the methane family ions: rate coefficients and implications

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

“…All other rate constant determinations were carried out at T e = 300 K (Canosa et al 1991;Geoghegan et al 1991;Mahdavi et al 1971) or within a reduced temperature range (Kasner 1967). Interestingly, more recent studies from Peterson et al (1998) and Sheehan & St. Maurice (2004) who measured cross sections using merged beam techniques led to the same electron temperature dependence of k (k(T e ) ∼ T −0.39 e ) for T e < 1200 K (Sheehan & St. Maurice 2004), but for a population of ions in several vibrational states among which the ground state accounted for about 50%. This observation suggests that the vibrational excitation of the ions has probably little influence on the electron temperature dependence below 1200 K. It is worth indicating however that recent merged beam experiments demonstrated that the electron temperature dependence may be non-monotonic.…”

“…The only available work is a quantum-theoretical calculation from Guberman (2003) who indicated that at room temperature the rate constant is 2.6 × 10 −7 cm 3 s −1 and at 1000 K 1.6 × 10 −7 cm 3 s −1 . For ions in vibrational excited states, however, there are no experiments that allow clear conclusions, because ions are formed in a mixture of different vibrational states (Peterson et al 1998;Sheehan & St. Maurice 2004;Zipf 1980, Zipf (1980 made a study in which he identified the v = 0, 1, and 2 levels by laser-induced fluorescence and reported rate constants at 300 K, which were increasing with the excitation level. However, it was recognised later that his experiment reflected the effective recombination for N + 2 ions with a vibrational temperature near 1500 K. Reanalysis of this work by Bates & Mitchell (1991) led to the qualitative conclusion that, at 300 K, the rate constant for the dissociative recombination of N + 2 (v = 1, 2) should be much smaller than for the ground state.…”

“…From an experimental point of view, two classes of studies have been carried out: those measuring directly the rate constant k (Canosa et al 1991;Cunningham & Hobson 1972;Geoghegan et al 1991;Kasner 1967;Mahdavi et al 1971;Mehr & Biondi 1969;Zipf 1980) and those which determined cross sections as a function of the relative energy of the N + 2 ions and electrons (Kella et al 1996;Mul & McGowan 1979;Noren et al 1989;Oddone et al 1997;Peterson et al 1998;Sheehan & St. Maurice 2004). The latter were then able to derive a rate constant by averaging the cross section over a Maxwellian energy distribution.…”

“…They have observed only dissociative charge transfer products with branching ratios (T e /300) −0.39 cm 3 s −1 (±25%). The dissociative recombination of N + 2 has been extensively studied, both experimentally (Canosa et al 1991;Cunningham & Hobson 1972;Geoghegan et al 1991;Kasner 1967;Kella et al 1996;Mahdavi et al 1971;Mehr & Biondi 1969;Mul & McGowan 1979;Noren et al 1989;Oddone et al 1997;Peterson et al 1998;Queffelec et al 1985;Sheehan & St. Maurice 2004;Zipf 1980) and theoretically (Guberman 1991(Guberman , 2003(Guberman , 2012Guberman et al 1993). The interest in the reaction arises because of its involvement in Earth's atmosphere photochemistry (Fox & Dalgarno 1985;Torr & Torr 1979), and more generally in the chemistry of terrestrial planet ionospheres (Fox 1992(Fox , 1993Fox et al 1993).…”

Computed bound and continuum electronic states of the nitrogen molecule

“…Collisional quenching has proven to be inefficient in cooling the system to its ground state [2]. As a result only limited and relatively uncertain data is available experimentally for this process [3,4]. Furthermore, re-entry studies require DR data not just for the vibrational ground state but for a range of vibrationally excited state.…”