Resonant Auger decay of the core-excited C*O molecule in intense x-ray laser fields

Abstract

The dynamics of the resonant Auger (RA) process of the core-excited C * O(1s −1 π * , v r = 0) molecule in an intense X-ray laser field is studied theoretically. The theoretical approach includes the analogue of the conical intersections of the complex potential energy surfaces of the ground and 'dressed' resonant states due to intense X-ray pulses, taking into account the decay of the resonance and the direct photoionization of the ground state, both populating the same final ionic states coherently, as well as the direct photoionization of the resonance state itself. The light-induced non-adiabatic effect of the analogue of the conical intersections of the resulting complex potential energy surfaces gives rise to strong coupling between the electronic, vibrational and rotational degrees of freedom of the diatomic CO molecule. The interplay of the direct photoionization of the ground state and of the decay of the resonance increases dramatically with the field intensity.The coherent population of a final ionic state via both the direct photoionization and the resonant Auger decay channels induces strong interference effects with distinct patterns in the RA electron spectra. The individual impact of these physical processes on the total electron yield and on the CO + (A 2 Π) electron spectrum are demonstrated.

Nonlinear resonant Auger spectroscopy in CO using an x-ray pump-control scheme

“…Since the wave-packet dynamics in the present study evolve around the equilibrium 063413-2 region of the CO molecule, it would be a good approximation to neglect the nuclear coordinate dependence of those parameters, explicitly, d 1 = 0.1 a.u., d 2 = 0.03 a.u., and V = 0.007 a.u. [25].…”

“…A |1/r 12 | R is the Coulomb matrix element between the core-excited state and the final ionic state, Aug = 2π |V | 2 is the Auger decay width, which is 0.08 eV in the case considered, corresponding to an Auger lifetime of about 8.2 fs, and − i 2 ph (t) represents the time-dependent leakage due to direct photoionization [25,26]. Since the wave-packet dynamics in the present study evolve around the equilibrium 063413-2 region of the CO molecule, it would be a good approximation to neglect the nuclear coordinate dependence of those parameters, explicitly, d 1 = 0.1 a.u., d 2 = 0.03 a.u., and V = 0.007 a.u.…”

“…The time-dependent norm of X (t) corresponds to the time-dependent occupation probabilities of the electronic state X = (I,R,F,A). In the ansatz of the total wave function we separated a rapid-evolving phase factor e −iω 1 t or e −i(ω 1 −ω 2 )t [25,26,[40][41][42][43].…”

“…The time-dependent wave-packet-propagation method [25,26,39] is employed to evaluate the dynamics of the electronic states and the RAS spectrum. Within the BornOppenheimer approximation, the total wave function (t), including the four electronic states (the ground, resonant, and final valance excited sates with the stationary electronic wave functions I , R , and F , respectively, and the ionic state produced by the emission of Auger electrons of energy ε and electronic wave function ε A ) can be expanded as (t) = I (t) I + R (t)e…”

“…Due to this, we call the probe pulse the control pulse in what follows. Note that the Auger spectra can be changed with only one strong pump pulse (maybe with a further weak probe pulse), Rabi splitting appears in the spectra as studied in the atomic and molecular cases [24][25][26][27]; however, with the present weak-pump strong-control scheme, as the study shows, we can get the degree to control the Auger spectra. The core-excited state R has a short lifetime and predominantly decays via Auger decay, resulting in the so-called resonant Auger scattering (RAS) process.…”