Orientation-angle-resolved photoelectron angular distribution in dissociative ionization of methanol induced by an intense ultraviolet laser pulse

Abstract

We investigate dissociative ionization of methanol, $\mathrm{C}{\mathrm{H}}_{3}\mathrm{OH}\ensuremath{\rightarrow}{\mathrm{CH}}_{3}{}^{+}+\mathrm{OH}+{e}^{\ensuremath{-}}$, in a linearly polarized intense ultraviolet laser field (400 nm, 67 fs, $3.1\ifmmode\times\else\texttimes\fi{}{10}^{13}\phantom{\rule{0.28em}{0ex}}\mathrm{W}/\mathrm{c}{\mathrm{m}}^{2}$) by photoelectron-photoion coincidence three-dimensional momentum imaging. The photoelectron angular distributions (PADs) are recorded as a function of the orientation angle between the molecular C-O bond axis and the laser polarization direction. Photoelectrons are emitted dominantly along the laser polarization direction when ${\mathrm{CH}}_{3}{\mathrm{OH}}^{+}$ is produced in the $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{X}$ state via the four-photon absorption. By contrast, the photoelectron emission becomes prominent along the direction perpendicular to the laser polarization direction when ${\mathrm{CH}}_{3}{\mathrm{OH}}^{+}$ is produced in the $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{B}$ state via the five-photon absorption. The orientation-angle-resolved PADs are expanded in terms of spherical harmonics in the laboratory frame, and then the anisotropy of the PADs varying as a function of the orientation angle of the C-O bond axis with respect to the laser polarization direction is examined quantitatively. We discuss how the shape of the molecular orbital from which an electron is emitted is reflected in the recorded PADs.