Two-dimensional fragment ion momentum distributions for dissociation channels of (a) C2H22+ → H++C2H+, (b) C2H22+ → CH++CH+, (c) C2H22+ → C++CH2+ and (d) C2H23+ → H++C2H2+

Figure 3. Two-dimensional fragment ion momentum distributions for dissociation channels of (a) C2H22+ → H++C2H+, (b) C2H22+ → CH++CH+, (c) C2H22+ → C++CH2+ and (d) C2H23+ → H++C2H2+. The polarization vector ε of the light and time-of-flight direction of fragments are marked as P and P directions, respectively. The third momentum component P3 along the third coordinate (the propagation direction of the FEL) was integrated over |P3| < 40 au in (a), |P3| < 20 au in (b), (c) and |P3| < 15 au in (d). Furthermore, events with |P| < 12 au are removed in (a) due to false H+ events resulting from H2O and H2 in the vacuum, and events with |P| < 12 au are removed in (c) due to a strong mixture with the CH++CH+ channel.

Abstract

Few-photon induced ultrafast dynamics in acetylene (C2H2) leading to several dissociation channels—deprotonation (H++C2H+ and H++C2H2+), symmetric break-up (CH++CH+) and isomerization (C++CH2+)-–were investigated employing the (XUV; extreme ultra-violet)-pump–(XUV; extreme ultra-violet)-probe scheme at the free-electron laser in Hamburg, combined with multi-hit coincidence detection. The kinetic energy releases and fragment-ion momentum distributions for various decay channels are presented. The C++CH2+ and H++C2H2+ channels reveal clear signatures of ultrafast molecular mechanisms, demonstrating potential applications of our pump-probe technique to complex systems in order to study a large variety of ultrafast phenomena in the XUV regime.