Theoretical investigation of alignment-dependent intense-field fragmentation of acetylene

Abstract

We analyze the alignment-dependent dissociative and nondissociative ionization of acetylene, ${\mathrm{C}}_{2}{\mathrm{H}}_{2}$. Numerical models describing the yield of the singly and doubly charged ions $({\mathrm{C}}_{2}{\mathrm{H}}_{2}{}^{+},{\mathrm{C}}_{2}{\mathrm{H}}_{2}{}^{2+})$ and several fragmentation and isomerization channels $({\mathrm{C}}_{2}{\mathrm{H}}^{+}+{\mathrm{H}}^{+},{\mathrm{CH}}^{+}+{\mathrm{CH}}^{+},{\mathrm{CH}}_{2}{}^{+}+{\mathrm{C}}^{+})$ as a function of the relative alignment angle between the laser polarization axis and the molecular axis are presented. We apply and compare two different approaches. The first is based on time-dependent density functional theory. The second is a quasi-single-particle approach using the Dyson orbitals. We find good agreement between the results of both methods. A comparison of our theoretical predictions with experimental data allows us to show that the alignment-dependent yield of most reaction channels is described to high accuracy assuming sequential ionization. However, for some of the fragmentation channels, namely, ${\mathrm{CH}}^{+}+{\mathrm{CH}}^{+}$ and ${\mathrm{C}}_{2}{\mathrm{H}}^{+}+{\mathrm{H}}^{+}$, we find non-negligible influence of recollisional ionization.