Formation of heterogeneous clusters in superfluid helium nanodroplets: phthalocyanine and water.

Clusters consisting of a single phthalocyanine molecule and a single water molecule are investigated by means of electronic spectroscopy in superfluid helium droplets. A recent spectroscopic study of those clusters [J. Fischer, F.

Electronic spectroscopy of phthalocyanine in a supersonic jet revisited.

Spectroscopic investigation of phthalocyanine in the gas phase has tremendously profited from molecular beam spectroscopy. Isentropic expansion succeeds in reducing the population of rovibrational states to the vibrational ground state so that only low energy rotational states remain populated. However, with respect to UV-vis spectroscopy the pioneers of molecular beam spectroscopy came to the discouraging conclusion that the information contained in the rotational structure of a large molecule is minimal, and even if the rotational structure could be resolved with great effort, the results are unlikely to be worth the difficulty [Levy, , 1980, 197-225].

Electronic Spectroscopy of Phthalocyanine and Porphyrin Derivatives in Superfluid Helium Nanodroplets.

Phthalocyanine and porphyrin were among the first organic compounds investigated by means of electronic spectroscopy in superfluid helium nanodroplets. Superfluid helium nanodroplets serve as a very gentle host system for preparing cold and isolated molecules. The uniqueness of helium nanodroplets is with respect to the superfluid phase which warrants the vanishing viscosity and, thus, minimal perturbation of the dopant species at a temperature as low as 0.

Microsolvation of molecules in superfluid helium nanodroplets revealed by means of electronic spectroscopy.

The empirical model explaining microsolvation of molecules in superfluid helium droplets proposes a non-superfluid helium solvation layer enclosing the dopant molecule. This model warrants an empirical explanation of any helium induced substructure resolved for electronic transitions of molecules in helium droplets. Despite a wealth of such experimental data, quantitative modeling of spectra is still in its infancy.

Impulsive laser induced alignment of molecules dissolved in helium nanodroplets.

We show that a 450 fs nonresonant, moderately intense, linearly polarized laser pulse can induce field-free molecular axis alignment of methyliodide (CH(3)I) molecules dissolved in a helium nanodroplet. Time-resolved measurements reveal rotational dynamics much slower than that of isolated molecules and absence of the sharp transient alignment recurrences characteristic of gas phase molecules. Our results presage a range of new opportunities for exploring both molecular dynamics in a dissipative environment and the properties of He nanodroplets.

Vibrations and hydrogen bonding in porphycene.

Combined use of IR, Raman, neutron scattering and fluorescence measurements for porphycene isolated in helium nanodroplets, supersonic jet and cryogenic matrices, as well as for solid and liquid solutions, resulted in the assignments of almost all of 108 fundamental vibrations. The puzzling feature of porphycene is the apparent lack of the N-H stretching band in the IR spectrum, predicted to be the strongest of all bands by standard harmonic calculations. Theoretical modeling of the IR spectra, based on ab initio molecular dynamics simulations, reveals that the N-H stretching mode should appear as an extremely broad band in the 2250-3000 cm(-1) region.

Photolysis of tert-butylthionitrite via excitation to the S(1) and S(2) states studied by 3d-REMPI spectroscopy.

S-Nitrosothiols serve as carriers and donors of NO in several important biological signaling systems. In these compounds the S-NO bond is rather labile and NO can be released thermally or photochemically. This paper reports on the photolytical decomposition of tert-butylthionitrite (t-BuSNO) in the visible and near-UV spectral regions.

Velocity resolved REMPI spectroscopy: a new approach to the study of photodissociation dynamics.

A new data acquisition mode has been implemented to a velocity-map ion-imaging setup, which records the velocity distributions of molecular photofragments with vibrational and rotational resolution. Compared to conventional velocity-map ion-imaging, the acquired data are of remarkable brilliance. This allows for unambiguous assignment of the fragment quantum states and the analysis of all rotational bands apparent in the electronic transition of the molecular fragment.

Rapidly pulsed helium droplet source.

A pulsed valve connected to a closed-cycle cryostat was optimized for producing helium droplets. The pulsed droplet beam appeared with a bimodal size distribution. The leading part of the pulse consists of droplets suitable for doping with molecules.

Mode-selective promotion and isotope effects of concerted double-hydrogen tunneling in porphycene embedded in superfluid helium nanodroplets.

Intramolecular double-hydrogen tunneling in porphycene (see picture) is investigated. Low-temperature conditions are ensured by doping of single molecules into superfluid helium nanodroplets. The investigation of fluorescence excitation and dispersed emission spectra and the highly dissipative environment allows the observation of mode-selective tunneling splitting and reveals a purely concerted tunneling mechanism for all isotopic variants of porphycene.

Structure and dynamics of phthalocyanine-argonn (n = 1-4) complexes studied in helium nanodroplets.

Van der Waals clusters of phthalocyanine with 1-4 argon atoms formed inside superfluid helium nanodroplets have been investigated by recording fluorescence excitation spectra as well as emission spectra. The excitation spectra feature a multitude of sharp lines when recorded in superfluid helium droplets in contrast to the respective spectra measured in a seeded supersonic beam (Cho et al. Chem.

Microsolvation of phthalocyanines in superfluid helium droplets.

Experimental and theoretical investigations of the spectroscopy of molecules in superfluid helium droplets provide evidence for the key role of the first helium layer surrounding the dopant molecule in determining the molecule's spectroscopic features. Recent investigations of emission spectra of phthalocyanine in helium droplets revealed a doubling of all transitions. Herein, we present the emission spectra of Mg-phthalocyanine and of phthalocyanine-argon clusters in helium droplets, which confirm the splitting as a general effect of the helium environment.