Photo-ion photo-electron coincidence study of methanol fragmentation by XUV pump and NIR probe pulses

Ionization and fragmentation of a methanol molecule has been studied in a pump probe experiment employing coincident velocity map imaging of resulting photoions and photoelectrons. The molecules photoionized by a 30 fs XUV high harmonics pulse were dissociated or further ionized by a near-infrared (790 nm) probe pulse arriving at variable time delays. The channel-selective yields, kinetic energies and angular distributions of the photoions and photoelectrons were recorded as a function of XUV-NIR delay. We compare the results obtained employing a single (13$^{\mathrm{th}})$ harmonic or a train of harmonics (13$^{\mathrm{th}}$ to 27$^{\mathrm{th}})$. While in the former case the outcome of the experiment is dominated by the dynamics in low-lying cationic states and the final products are mainly singly charged, the latter configuration often results in double ionization and populates many highly-excited cationic states. We observe H$_{\mathrm{3}}^{\mathrm{+}}$ ion formation in both singly or doubly charged final states, and trace signatures of hydrogen migration resulting in the ejection of OH$_{\mathrm{2}}^{\mathrm{+}}$ and OH$_{\mathrm{3}}^{\mathrm{+}}$ fragments.