Masaaki Tsubouchi

Femtosecond photoelectron imaging on pyrazine: Spectroscopy of 3s and 3p Rydberg states

Two-color and one-color resonance enhanced multiphoton ionization photoelectron spectroscopies (REMPI–PES) have been applied to Rydberg states (n=3) of jet-cooled pyrazine. The 3s and 3p members of Rydberg series converging to the ground state (n−1) of the cation and the 3s member of a Rydberg series converging to an excited state of the cation (π−1) were observed. The photoelectron angular distributions (PADs) measured via the 3s(n−1) state drastically differed for the two-color and one-color REMPI experiments. This behavior is ascribed to different molecular axis alignments created by the two-photon excitation schemes. The PADs were also used to discriminate between the different Rydberg series.

Femtosecond time-resolved charged particle imaging studies of the ultraviolet photodissociation of the NO dimer

Ultraviolet photodissociation dynamics of the NO dimer into NO(Α)+NO(Χ) in a supersonic molecular beam is studied by femtosecond pump-probe charged particle imaging. Time-resolved photoelectron imaging reveals that photoionization from the Franck–Condon region of the excited state(s) reaches vibrationally excited states of the NO dimer cation, resulting in spontaneous fragmentation into NO+NO+ even at the shortest pump-probe time delays. The corresponding photoelectron energy distribution extending up to more than 1 eV above the ionization threshold indicates a large structural difference between the dimer cation and the photoexcited neutral state. From the isotropic photoelectron distribution, this state is assigned to a valence state rather than a Rydberg state. The characteristic photoelectron distribution and also the small NO dimer ion signal vanish within 200 fs. In the same time the photoelectron image rapidly evolves from an almost isotropic distribution into an anisotropic one characteristic for ...

Photoelectron kinetic energy dependence in near threshold ionization of NO from A state studied by time-resolved photoelectron imaging.

Photoelectron angular distributions in the laboratory frame (LF-PADs) from the A((2)sigma(+)) state of NO molecule were measured by femtosecond time-resolved photoelectron imaging with (1 + 1()) resonance enhanced multiphoton ionization via the A state. High-precision measurements of the anisotropy parameters of LF-PADs were performed for the photoelectron kinetic energy from 0.03 to 1.05 eV as a function of the pump-probe delay time. The revival feature of the rotational wave packet on the A state was clearly observed in the time dependence of the photoelectron anisotropy parameters. By approximating the phase shifts of the photoelectron partial waves by the quantum defects in the high-lying Rydberg states using the multichannel quantum defect theory, the energy-dependent photoionization transition dipole moments were determined, for the first time, from time-dependent LF-PADs measured by time-resolved photoelectron spectroscopy.

Laser induced fluorescence spectroscopy of tetracene with large Ar, Ne, and H2 clusters in superfluid He nanodroplets.

Clusters of tetracene molecules with different numbers of attached (Ar)(N), (Ne)(N) and (H(2))(N) particles (N = 1-2000) are assembled inside superfluid He nanodroplets and studied via laser-induced fluorescence. The frequency shift of the fluorescence spectrum of the tetracene molecules is studied as a function of cluster size and pickup order of tetracene and cluster species. For (Ar)(N) and (Ne)(N) clusters, our results indicate that the tetracene molecules reside inside the clusters when tetracene is captured by the He nanodroplet before the cluster species; conversely, the tetracene molecules stay on the surface of the clusters when tetracene is captured after the cluster species. In the case of (H(2))(N) clusters, however, tetracene molecules reside inside the (H(2))(N) clusters irrespective of the pickup order. We conclude that (Ar)(N) and (Ne)(N) clusters are rigid at T = 0.38 K, while (H(2))(N) clusters of up to N = 2000 remain fluxional at the same temperature. The results may also indicate the occurrence of heterogeneous nucleation of the (H(2))(N) clusters, which is induced by the interaction with tetracene chromophore molecules.

One- and two-color photoelectron imaging of the CO molecule via the B 1Σ+ state

This paper is concerned with photoelectron imaging following one-color (2+1) and two-color (2+1′) resonance enhanced multiphoton ionization in the CO molecule. After the two-photon absorption step Bu200a1Σ+u200a(v′=0)←←Xu200a1Σ+u200a(v″=0) or Bu200a1Σ+u200a(v′=1)←←Xu200a1Σ+u200a(v″=0), the subsequent one-photon ionization Xu200a2Σ+(v+)←Bu200a1Σ+u200a(v′=0,1) shows deviations from the expected Δv=0 Franck–Condon propensity rule. The results are in good agreement with a previous study using time-of-flight photoelectron spectroscopy [Sha et al., J. Chem. Phys. 99, 4334 (1993)]. The experimental photoelectron kinetic energy spectra and their angular distributions are analyzed, and the essential role played by “superexcited” Rydberg states with an Au200a2Π ion core in this process is examined. Moreover, photoelectron imaging methods appear to be useful in extracting information about superexcited states.