Fragmentation of multiply charged hydrocarbon molecules CnHq+ (n ≤ 4, q ≤ 9) produced in high-velocity collisions: Branching ratios and kinetic energy release of the H+ fragment
Résumé
Fragmentation branching ratios for channels involving H+ emission and associated kinetic energy release of the H+ fragment [KER(H+)] have been measured for multicharged CnHq+ molecules produced in high velocity (3.6 a.u.) collisions between CnH+ projectiles and helium atoms. For CHq+ (q ≤ 4) molecules, measured KER(H+) were found well below predictions of the simple point charge Coulomb model (PCCM) for all q values. Multireference configuration interaction (MRCI) calculations for ground as well as electronic excited states were performed which allowed a perfect interpretation of the CHq+ experimental results for low charges (q = 2-3) as well as for the highest charge (q = 4). In this last case we could show, on the basis of ionization cross sections calculations and experimental measurements performed on the same systems at slightly higher velocity (4.5 a.u.), the prominent role played by inner-shell ionization followed by Auger relaxation and could extract the lifetime of this Auger relaxation giving rise to the best agreement between the experiment and the calculations. For dissociation of C2Hq+ and C3Hq+ with the highest charges (q ≥ 5), inner-shell ionization contributed in a prominent way to the ion production. In these two cases it was shown that measured KER(H+) were in good agreement with PCCM predictions when those were corrected for Auger relaxation with the same Auger lifetime value as in CH3+.