Ultrafast Evolution of Imidazole after Electronic Excitation

The ultrafast dynamics of the imidazole chromophore has been tracked after electronic excitation in the 250–217 nm energy region, by time delayed ionization with 800 nm laser pulses. The time-dependent signals collected at the imidazole⁺ mass channel show the signature of femtosecond dynamics, originating on the πσ*- and ππ*-type states located in the explored energy region. The fitting of the transients, which due to the appearance of nonresonant coherent adiabatic excitation requires a quantum treatment based in the Bloch equations, yields two lifetimes of 18 ± 4 and 19 ± 4 fs. The first is associated with the πσ* ← ππ* internal conversion, while the second reflects the loss of ionization cross-section as the system evolves along the dissociative πσ* surface. This study provides a comprehensive picture of the photophysics of the molecule that agrees with previous experimental and theoretical findings