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

Abstract

We measure the photoionization cross-section of vibrationally excited levels in the S 2 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 welldefined 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. (1) we unambiguously assign the fast initial decay signal to rotational dephasing of the initial alignment created by the pump transition.

Communication: Existence of the doubly excited state that mediates the photoionization of azulene

“…The photoelectron spectra of azulene recorded in the 1 + 2 time-resolved photoelectron imaging experiments 1 (see Ref. 19 for a related study) are invariant (apart from the intensity) with respect to the pump-probe delay time and wavelength of the pump pulse (see Fig. 1 and Ref.…”

“…1, independent of the pump wavelength. Furthermore, to rationalize the optically induced anisotropy associated with the pump excitation, 19 the postulated doubly excited state should represent a totally symmetric singlet excitation accessible from S 2 and, considering the well-understood electronic structure of the ionized azulene, 20 have an electron configuration dominated by the (HOMO) It should be mentioned that the multi-photon ionizaton of azulene from S 2 via unstable superexcited valence states relaxing to the Rydberg states prior to the final photoionization event has also been discussed in Ref. 3, but without determining a precise makeup of the hypothetical superexcited states.…”

Time-Resolved Photodetachment Anisotropy: Gas-Phase Rotational and Vibrational Dynamics of the Fluorescein Anion

“…Indeed, the interpretation of time-resolved photoelectron spectroscopic data can sensitively depend on such dynamics and rotational dynamics have been misinterpreted as population dynamics. 44,45 Simply measuring the total ion yield with two polarizations would eliminate such ambiguities. In cases where population dynamics are occurring on very different timescales as rotational dephasing, as is the case for nucleotides and oligonucleotides 46,47 for example, such complications are less important.…”

Des états super-excités vers une empreinte Rydberg

“…Cette invariance est reliée uniquement aux propriétés des états de Rydberg strictement parallèles à l'état de l'ion. Cette ionisation nous a permis de détecter l'anisotropie d'excitation de l'azulène [25]. …”