<em>Top panels</em>: measured yield of Se and C ion coincidences for (a) methylselenol at 2 keV and (c) ethylselenol at 1.7 keV photon energy

<p><strong>Figure 3.</strong> <em>Top panels</em>: measured yield of Se and C ion coincidences for (a) methylselenol at 2 keV and (c) ethylselenol at 1.7 keV photon energy. For ethylselenol, the yields of triple coincidences of Se-ions with both carbon ions (the combinations are indicated at the axis) are shown. Note that the Se<sup>7+</sup>C<sup>1+</sup> and Se<sup>7+</sup>C<sup>2+</sup> coincidence channels in methylselenol and all coincidence combinations of Se<sup>7+</sup> with C<sup>1+</sup> in ethylselenol had to be omitted in the analysis due to significant contributions of false coincidences from the residual background gas. <em>Bottom panels</em>: the total charge induced on the (b) methylselenol and (d) ethylselenol molecules compared to the charge state distribution observed in krypton at 2 keV photon energy under the same experimental conditions. The heavy ion charge represents the sum of Se and C charges measured in coincidence, whereas the CH<sub>3</sub>SeH and C<sub>2</sub>H<sub>5</sub>SeH charge denotes the total charge of the molecule assuming that four or six H<sup>+</sup> ions were produced, respectively.</p> <p><strong>Abstract</strong></p> <p>The ionization and fragmentation of two selenium containing hydrocarbon molecules, methylselenol (CH<sub>3</sub>SeH) and ethylselenol (C<sub>2</sub>H<sub>5</sub>SeH), by intense (>10<sup>17</sup> W cm<sup>−2</sup>) 5 fs x-ray pulses with photon energies of 1.7 and 2 keV has been studied by means of coincident ion momentum spectroscopy. Measuring charge states and ion kinetic energies, we find signatures of charge redistribution within the molecular environment. Furthermore, by analyzing fragment ion angular correlations, we can determine the laboratory-frame orientation of individual molecules and thus investigate the fragmentation dynamics in the molecular frame. This allows distinguishing protons originating from different molecular sites along with identifying the reaction channels that lead to their emission.</p>