Angular and energy distribution of fragment ions in dissociative double photoionization of acetylene molecules at 39 eV

The two-body dissociation reactions of the dication, C2H22+, produced by 39.0 eV double photoionization of acetylene molecules, have been studied by coupling photoelectron-photoion-photoion coincidence and ion imaging techniques. The results provide the kinetic energy and angular distributions of product ions. The analysis of the results indicates that the dissociation leading to C2H++H+ products occurs through a metastable dication with a lifetime of 108 ± 22 ns, and a kinetic energy release (KER) distribution exhibiting a maximum at ~4.3 eV with a full width at half maximum (FWHM) of about 60%. The reaction leading to CH 2++C+ occurs in a time shorter than the typical rotational period of the acetylene molecules (of the order of 10-12 s). The KER distribution of product ions for this reaction, exhibits a maximum at ~4.5 eV with a FWHM of about 28%. The symmetric dissociation, leading to CH+ + CH+, exhibits a KER distribution with a maximum at ~5.2 eV with a FWHM of 44%. For the first two reactions the angular distributions of ion products also indicate that the double photoionization of acetylene occurs when the neutral molecule is mainly oriented perpendicularly to the light polarization vector.