State-to-state dissociation photoionization of molecular nitrogen : the full story

N2 is a major constituent of Earth and planetary atmospheres.
First, evidenced in 1952, the dissociative photoionization
of molecular nitrogen, N2, plays an important
role in the species abundance, out of equilibrium evolution,
and chemical reactivity of diverse media including
upper atmospheres (the so-called ionospheres) and
plasma. Many scenarios were proposed for rationalizing
the dissociative ionization mechanisms and exit channels,
which are reviewed here, mainly involving the N2
+
(C2Σu
+, v+) vibrational levels state-to-state dynamics on
which we focus. We show, however, that previous studies
are not comprehensive enough for fully shedding
light on the complex undergoing processes. As
a complementary global work, we used state-of-the-art
quantum chemistry, time dependent and independent
theoretical approaches associated to advanced experimental
techniques to study the unimolecular decomposition
of the N2
+ ions forming the N+ + N products. In
addition to the already suggested spin-orbit-induced
predissociation of the cationic C2Σu
+ state, we documented
a new mechanism based on vibronic coupling and
tunneling dissociation. Besides, the quantum processes
highlighted here should be also in action in the
dynamics of electronically excited larger molecular systems
involved in physical and chemical phenomena in
plasma and in various natural environments on Earth
and beyond.