Ion-Molecule Reactions of ArN2+ with Butane and Isobutane at Thermal Energy

Abstract

Listen

Translate article

Abstract Product ion distributions and rate constants have been determined for thermal energy reactions of ArN2+ with n-C4H10 and i-C4H10 by using an ion-beam apparatus. C4H9+, C3Hn+ (n = 5—7), and C2Hn+ (n = 4,5) are produced from n-C4H10 with branching ratios of 6, 57, and 37%, while C4H9+ and C3Hn+ (n = 5—7) are formed from i-C4H10 with branching ratios of 13 and 87%, respectively. A comparison of the product ion distribution in the ArN2+/n-C4H10 reaction with that predicted from the fragmentation pattern of n-C4H10+ suggests that most of all fragment ions are formed through (pre)dissociation of precursor n-C4H10+ states at ca. 13.2 eV. Since this energy is close to the effective recombination energy of ArN2+ (ca. 13.5 eV), it is concluded that the ArN2+/n-C4H10 dissociative charge-transfer reaction proceeds through near-resonant n-C4H10+ states. The total rate constants are (6.9 ± 2.3) × 10−10 cm3 s−1 for n-C4H10 and (9.0 ± 2.6) × 10−10 cm3 s−1 for i-C4H10, which amount to 58 and 75% of the collision rate constants estimated from Langevin theory, respectively.