Following coherent multichannel nuclear wave packets in pump-probe studies of O2 with ultrashort laser pulses

Abstract

We reexamine the recent pump-probe experiment with O2 using short intense infrared laser pulses theoretically. Using parameters that closely mimic the experimental conditions and taking into account the angle-dependent population redistribution due to resonant coupling between the relevant states, we show that the observed kinetic energy release spectra, including the energy-dependent structure and the quantum beat frequencies, can be accurately reproduced. Our results reveal additional important channels that were missed out earlier. In particular, the strong contributions from O + 2 a 4 Πu and b 4 Σ − g states lead to the possibility of observing the inter-channel beating. We further demonstrate that, by varying the laser parameters, the coherent nuclear wave packet motions on different potential energy surfaces (PESs) can be probed and the properties of the PES can be examined. Future experiments with different wavelength lasers are proposed for better probing and controlling nuclear dynamics on different PESs.

Molecular bond stabilization in the strong-field dissociation of O2+

“…It thus leaves the shape of the initial cationic nuclear wave packet undetermined [7,8]. Cationic vibrational-state distributions calculated in FC approximation tend to be vibrationally warmer than those obtained by modeling the initial ionization process based on molecular Ammosov-Delone-Krainov (ADK) tunneling-ionization rates [3,6].…”

“…The prominence of hydrogen molecular ions for time-resolved pump-probe studies of their excited nuclear dynamics extends to the development of computational and analytical techniques. Examples for these techniques are, respectively, the representation of the external-field-dressed molecular structure in terms of adiabatic BO-Floquet molecular potential surfaces [2,28,30] and the quantum-beat analysis in the frequency domain of time-resolved fragment KER spectra [1,3,6,11,12,14,15,19] which we apply in this work.…”

“…In many cases, the intramolecular nuclear dynamics in the excited molecular ions can be described in terms of nuclear wave packets that are generated by ionization of the parent molecule and represented as coherent superpositions of ro-vibrational stationary states in several adiabatic Born-Oppenheimer (BO) electronic states of the external-fieldfree molecular ion (see, e.g., Refs. [1][2][3][4][5]…”

State-selective dissociation dynamics of an oxygen molecular ion studied with single-harmonic pump and infrared-probe pulses

“…Therefore, as discussed in Ref. [13,[17][18][19][54][55][56], the 2 pathway most likely occurs via one of the two following pathways. The first one proceeds via the resonant absorption of three NIR photons from the 4 u a  to the 4 g f  state, and subsequent stimulated emission of one NIR photon as the wave packet passes through the position of the resonant 1 transition between the two states as shown in Fig.…”

“…[13] pointed out a certain discrepancy between their measured frequencies of the wave packet vibrational motion and the expected frequencies for the corresponding vibrational levels of the 4 u a  state. In a recent theoretical analysis [56] this discrepancy was attributed to the contribution from the higher-lying 4 g b −  state of O2 + . Since this state is not accessible by our 17.3 eV pump photon, this state is unlikely to contribute significantly to the dissociation signal observed in our work.…”