Nicholas A. Miller, Aniruddha Deb, Roberto Alonso-Mori, James M. Glownia, Laura M. Kiefer, Arkaprabha Konar, Lindsay B. Michocki, Marcin Sikorski, Danielle L. Sofferman, Sanghoon Song, Megan J. Toda, Theodore E. Wiley, Diling Zhu, Pawel M. Kozlowski, Kevin J. Kubarych, James E. Penner-Hahn, and Roseanne J. Sension J. J. Phys. Chem. A (2018) 122, 4963-4971
Polarized ultrafast time-resolved X-ray absorption near edge structure (XANES) allows characterization of excited state dynamics following excitation. Excitation of vitamin B12, cyanocobalamin (CNCbl), in the αβ-band at 550 nm and the γ-band at 365 nm was used to uniquely resolve axial and equatorial contributions to the excited state dynamics. The structural evolution of the excited molecule is best described by a coherent ballistic trajectory on the excited state potential energy surface. Prompt expansion of the Co cavity by ca. 0.03 Å is followed by significant elongation of the axial bonds (>0.25 Å) over the first 190 fs. Subsequent contraction of the Co cavity in both axial and equatorial directions results in the relaxed S1 excited state structure within 500 fs of excitation.