Tracking Hole Migration Dynamics with X-Ray Attosecond Transient Absorption
Abstract
Photoinduced charge migration is a fundamental and ubiquitous phenomenon in chemistry, with applications in diverse areas including photosynthesis, photovoltaics, DNA-based nanoelectronics, and catalysis. Understanding these phenomena is key to the Chemical Sciences Program of the Army Research Office, with its focus on determining the pathways and intermediates for fast chemical reactions and energy transfer mechanisms in molecular systems. The charge migration dynamics induced by ionization, also known as Òhole dynamicsÓ, represent a purely electronic time scale in chemistry and occur on a timescale of less than 5 fs. As such, they can be probed using attosecond techniques available in our laboratory (1 attosecond=10-18 sec). In the proposed experiments, a few-cycle near infrared (NIR) pulse will ionize a target molecule by strong field ionization. The resulting hole dynamics will be probed by absorption of a broadband attosecond pulse, using attosecond transient absorption (ATA) spectroscopy at photon energies above 280 eV, the energy at which K-shell core-to-valence transitions in carbon become accessible. ATA in this soft x-ray region provides elemental specificity and is also sensitive to the charge state and chemical bonding environment of the atoms being probed. The proposed research focuses on three initial target systems: glycine, the simplest amino acid, uracil, the RNA nucleobase, and PENNA (2-phenylethyl-N,N-dimethylamine), a model system for hole transfer between two well-separated functional groups. All three molecules contain multiple chemically inequivalent first row atoms, each of which will have distinct and charge-sensitive core-to-valence transitions that can be probed in our experiment. In addition, PENNA is predicted to exhibit particularly pronounced hole migration dynamics upon ionization that result from electron correlation effects.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jul 09, 2020
- Source ID
- W911NF2010127
Entities
People
- Daniel Neumark
Organizations
- Army Contracting Command
- United States Army
- University of California, Berkeley