The kinetic energy release (KER) of molecular fragments is of major interest
in molecular reaction dynamics. When dissociation reactions of polyatomic ions occur,
some of the excess internal energy of the ion is released as kinetic energy of the two
fragments. The KER provides important information about the structures of the
molecular species involved and on the energetics and dynamics of the reaction. To
meet this end, the translational kinetic energy release distribution spectra of selected
ionic fragments, produced through dissociative single and double photoionization of
dichloromethane (DCM) molecule at photon energies around the chlorine L edge, were
measured from the shape and width of the experimentally obtained time-of-flight
(TOF) distributions. The kinetic energy release distributions (KERD) spectra exhibit
either smooth profiles or structures, depending on the ionic fragment and photon
wavelength. In general, the heavier the ionic fragments, the lower are their average
KERDs. In contrast, the light H+ fragments are observed with kinetic energies centered
around 4.5-5.5 eV, depending on the photon wavelength. It was noticed that the change
in the photon wavelength involves a change in the KERDs, pointing out different
processes or transitions taking place in the break-up process. In the particular case of
double ionization with the ejection of two charged fragments, the kinetic energy distri-butions present own characteristics compatible with the Coulombic fragmentation
model. Intending to interpret the experimental data singlet and triplet states at the
chlorine L edge of the dichloromethane molecule, associated to the Cl (2p → 10a1*)
and Cl (2p → 4b1*) transitions, were determined at multiconfigurational self-consistent
field (MCSCF) level and multi reference configuration interaction (MRCI). These
states were selected to form the spin-orbit coupling matrix elements, which after
diagonalization results in a spin-orbit manifold. Minimum energy pathways for
dissociation of the molecule were additionally calculated aiming to give support to the
presence of the ultra-fast dissociation mechanism in the molecular break-up.
Keywords: Fragmentation, PEPICO, PEPIPICO, Kinetic energy release, Timeof-
flight spectrometer, MCSCF, Spin-orbit, Cl 2p, Translational energy,
Photoions, Shallow core, Photoexcitation, Photoionization, Dichloromethane,
CH2Cl2.