ABSTRACT
Time-resolved photoelectron spectroscopy (TRPES) is a useful approach to elucidate the coupled electronic-nuclear quantum dynamics underlying chemical processes, but has remained limited by the use of low photon energies. Here, we demonstrate the general advantages of XUV-TRPES through an application to NO2, one of the simplest species displaying the complexity of a non-adiabatic photochemical process. The high photon energy enables ionization from the entire geometrical configuration space, giving access to the true dynamics of the system. Specifically, the technique reveals dynamics through a conical intersection, large-amplitude motion and photodissociation in the electronic ground state. XUV-TRPES simultaneously projects the excited-state wave packet onto many final states, offering a multi-dimensional view of the coupled electronic and nuclear dynamics. Our interpretations are supported by ab initio wavepacket calculations on new global potential-energy surfaces. The presented results contribute to establish XUV-TRPES as a powerful technique providing a complete picture of ultrafast chemical dynamics from photoexcitation to the final products.
ABSTRACT
Several recent studies have demonstrated how well-suited femtosecond time-resolved photoelectron spectra are for mapping wavepacket dynamics in molecular systems. Theoretical studies of femtosecond photoelectron spectra which incorporate a robust description of the underlying photoionization dynamics should enhance the utility of such spectra as a probe of wavepackets and of the evolution of electronic structure. This should be particularly true in regions of avoided crossings where the photoionization amplitudes and electronic structure may evolve rapidly with geometry. In this paper we present the results of studies of energy- and angle-resolved femtosecond photoelectron spectra for wavepackets in the diatomic systems, Na2 and NaI. Both cases involve motion through regions of avoided crossings. In Na2, however, wavepacket motion occurs on a single adiabatic potential with an inner and outer well and a barrier between them, while in NaI wavepackets move on the nonadiabatically coupled covalent (NaI) and ionic (Na+I-) potentials. Results of these studies will be used to illustrate the insight into wavepacket dynamics that time-resolved photoelectron spectra provide. For example, in the case of NaI these angle-resolved photoelectron spectra seem to offer some promise for probing real-time dynamics of intramolecular electron transfer occurring in the crossing region of the ionic and covalent states.
