Molecular Structure and Dynamics: Potential Energy Surfaces for Attosecond Spectroscopic Simulations.
Abstract
The time scale of the measurements determines the nature of the physical process that can be observed. Femptosecond measurements revel the dynamics of atoms in molecules including those involved in irreversible structural changes in chemical reactions while attosecond measurements reveal the dynamics of electron motion within atoms and molecules. With the recent technological advances to produce and probe attosecond pulses, attosecond spectroscopic measurements are an exciting new frontier for both experiment and theory. From the theoretician perspective attosecond processes are particularly challenging since the energy and the band width of the attosecond pulses are such that they can excite and ionize electrons from the core to the valence, covering energy ranges of several to thousands of electron volts. Molecular dynamics simulations of such processes require potential energy surfaces (PES) of electronic states with a vacant (or multiply vacant) core or inner valence orbitals. Yet such potential energy surfaces are virtually unknown. The examples presented in this proposal are the first to be reported. The objective of this proposal is to provide the methods and programs required to study such surfaces using predictive quality, state-of-the-art ab initio coupled-cluster methods. We demonstrate how coupled-cluster methods can be used to obtain the core-hole and other holestate potential surfaces and add several new features including spin-orbit effects, relativistic effects, vibronic corrections to PES, F12 basis set limit calculations, and extra orbital relaxation. The later becomes particularly important in core-hole states and core-excitation spectra. The combination provides the high-accuracy surfaces essential for time-dependent simulations. The featured applications, chosen from a list targeted for experiments, consist of saturated or unsaturated organic molecules (for example CH3Br, ICHCHBr, ICH2CH2Br) with I and Br atoms on the same or at different ends of the molecules, the Fe, Br, I, Xe, He atoms, any inter-halogen like FCl, Br2, BrCl, IBr, benzene and ethylene molecules. In particular, the charge resonance enhanced ionization phenomenon for homo-nuclear systems like I2, are of special interest. This effort is essential to develop the theory complement to the rapidly evolving field of attosecond spectroscopy.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Dec 04, 2018
- Source ID
- W911NF1610260
Entities
People
- Rodney J. Bartlett
Organizations
- Army Contracting Command
- United States Army
- University of Florida