PNNL

Abstract

The ultrafast photoinduced chirality loss of 2-iodobutane is studied theoretically by time- and frequency-resolved Xray circular dichroism (TRXCD) spectroscopy. Following an optical excitation, the iodine atom dissociates from the chiral center, which we capture by quantum non-adiabatic molecular dynamics simulations. At variable time delay after the pump, the resonant X-ray pulse selectively probes the iodine and carbon atom involved in the chiral dissociation through a selected core-to-valence transitions. We demonstrate that TRXCD can directly probe the molecular chirality and vibronic coherences, which are indirectly accessible in transient X-ray absorption spectroscopy. The TRXCD signal at the iodine L1 edge accurately captures the timing of C-I photodissociation and thereby chirality loss, occurring within 70 fs. The signals at the carbon Kedges monitor the molecular chirality the 2-butyl radical photoproduct, and the spin state of the iodine atom. The evolution of the core electronic states and chiral sensitivity with respect to the atomic positions is discussed. Overall, the element-specific TRXCD signal provides a detailed picture of molecular dynamics and offers a sensitive window into the time-dependent chirality of molecules.