Mode-Specific Vibrational Autodetachment Following Excitation of Electronic Resonances by Electrons and Photons

Abstract

Electronic resonances commonly decay via internal conversion to vibrationally hot anions and subsequent statistical electron emission. We observed vibrational structure in such an emission from the nitrobenzene anion, in both the 2D electron energy loss and 2D photoelectron spectroscopy of the neutral and anion, respectively. The emission peaks could be correlated with calculated nonadiabatic coupling elements for vibrational modes to the electronic continuum from a nonvalence dipole-bound state. This autodetachment mechanism via a dipole-bound state is likely to be a common feature in both electron and photoelectron spectroscopies.

Autodetachment dynamics of 2-naphthoxide and implications for astrophysical anion abundance

“…The dipole-bound state autodetaches through modespecific vibrational autodetachment invoked by modes that strongly couple the dipole-moment to the continuum. 31,33,36,37 These modes would be similar to the modes of the final neutral ground state. The lowest frequency mode of a 0 symmetry for the D 0 electronic state was calculated at n 33 = 310 cm À1 and is moderately infra-red active.…”

“…This vibrational mode satisfies the criterion for efficient electron ejection or 'shake off' when directly exciting the dipole-bound state -modulation of the dipole-bound state orbital by the vibrational motion -and would generate a similar (s-wave) low-eKE spectrum to mode-specific autodetachment proposed in mechanism (b). 33,[36][37][38][39][40][41] This detachment mechanism usually involves Dv = À1, where v is a vibrational level, although anharmonicity associated with low-frequency bending modes has shown that Dv = À2 also occurs in this system. 23 The proposed low frequency mode, n 33 , is likely to be populated at T E 300 K according to Boltzmann statistics.…”

“…It is worth mentioning that in the present experiment we optically prepared the same excited states that could be occupied through an electron capture mechanism. 24,37 From an experimental point of view, our approach has two key advantages over an electron capture experiment: (i) the ability to directly probe the dynamics using femtosecond laser strategies, and (ii) massselectivity through separation of anions using time-of-flight mass spectrometry.…”

Electron scattering cross sections from nitrobenzene in the energy range 0.4–1000 eV: the role of dipole interactions in measurements and calculations

“…Interconnections between valence states of anions and dipole-bound states have also been identified in the opposite direction (bifurcation of the excited state wavepacket leading to the formation of a non-valence state) for a common anionic chromophore, 55 and the stability of such orbitals in the presence of perturbing molecules has also been studied by the same group. 56 Very recently, Anstöter et al 57 showed that the observed emission peaks from the vibrational structure of the nitrobenzene anion can be correlated with an autodetachment mechanism via dipole-bound state formation. In all these cases, dipole-bound states are formed at very low energy, below the lower energy limit of the present experimental study (0.4 eV).…”

Nonadiabatic dynamics in multidimensional complex potential energy surfaces

“…The latter relaxation channel, dissociative electron attachment (DEA), is ubiquitous in molecules of various types, even though its underlying working mechanisms are far from understood. 19 Transient anions can also be populated by photoexcitation of an electronically bound anion, 20,21 possibly accessing different regions of the PESs and leading to distinct decaying channels. Related processes include dissociative recombination 22 and associative detachment, the latter being the inverse process of DEA.…”