Time-dependent photoionization of azulene: Optically induced anisotropy on the femtosecond scale

TL;DR

This study investigates the femtosecond-scale photoionization dynamics of azulene, revealing optically induced anisotropy and rotational dephasing effects through pump-probe spectroscopy.

Contribution

It provides the first detailed measurement of azuleme's photoionization cross-section and clarifies the origin of short-term transient signals as rotational dephasing.

Findings

Identification of polarization-dependent transient behaviors.

Observation of short-term rotational dephasing effects.

Distinction between short-term and long-term decay processes.

Abstract

We measure the photoionization cross-section of vibrationally excited levels in the S2 state of azulene by femtosecond pump-probe spectroscopy. At the wavelengths studied (349-265 nm in the pump) the transient signals exhibit two distinct and well-defined behaviours: (i) Short-term (on the order of a picosecond) polarization dependent transients and (ii) longer (10 ps - 1 ns) time-scale decays. This letter focuses on the short time transient. In contrast to an earlier study by Diau et al.22 [J. Chem. Phys. 110 (1999) 9785.] we unambiguously assign the fast initial decay signal to rotational dephasing of the initial alignment created by the pump transition.