@article{StromeckFaderlPentlehnerKensyetal.2011, author = {Stromeck-Faderl, A. and Pentlehner, Dominik and Kensy, U. and Dick, B.}, title = {High-resolution electronic spectroscopy of the BODIPY chromophore in supersonic beam and superfluid helium droplets}, series = {CHEM-PHYS-CHEM, Special Issue: Laser Chemistry and Spectroscopy}, journal = {CHEM-PHYS-CHEM, Special Issue: Laser Chemistry and Spectroscopy}, number = {12}, year = {2011}, abstract = {We present the fluorescence excitation and dispersed emission spectra of the parent compound of the boron dipyrromethene (BODIPY) dye class measured in a supersonic beam and isolated in superfluid helium nanodroplets. The gas-phase spectrum of the isolated molecules displays many low-frequency transitions that are assigned to a symmetry-breaking mode with a strongly nonharmonic potential, presumably the out-of-plane wagging mode of the BF2 group. The data are in good agreement with transition energies and Franck-Condon factors calculated for a double minimum potential in the upper electronic state. The corresponding transitions do not appear in the helium droplet. This is explained with the quasi-rigid first layer of helium atoms attached to the dopant molecule by van der Waals forces. The spectral characteristics are those of a cyanine dye rather than that of an aromatic chromophore.}, language = {en} } @article{PentlehnerGreilDicketal.2010, author = {Pentlehner, Dominik and Greil, Ch. and Dick, B. and Slenczka, Alkwin}, title = {Line broadening in electronic spectra of anthracene derivatives inside superfluid helium nanodroplets}, series = {The Journal of Chemical Physics}, journal = {The Journal of Chemical Physics}, number = {133}, year = {2010}, abstract = {Electronic spectroscopy of molecules profits greatly from superfluid helium droplets serving as a gentle cryogenic matrix. Characteristic features of electronic spectra in helium droplets are a solvent shift, phonon wings, and in rare cases a splitting of zero phonon lines. For the majority of molecules investigated so far in helium droplets the vibrational fine structure in electronic spectra resembles what was observed in a supersonic jet. The electronic spectra of three methylated anthracene derivatives and one phenylated anthracene discussed in this paper reveal remarkable effects in the vibrational fine structure due to solvation in helium droplets. For all four compounds the vibrational frequencies were almost not affected by the helium environment. However, if the electronic excitation is accompanied by nuclear rearrangement, the spectra showed remarkable line broadening in helium droplets. This is the case for 2-methylanthracene and 9-phenylanthracene. The corresponding line shape was of Lorentzian type and, thus, attributed to damping of the excited system by the helium environment. According to the linewidth the damping time constant was determined to be about 0.3 ps in the case of 2-methylanthracene and 0.1 ps for 9-phenylanthracene.}, language = {en} } @article{LehnigPentlehnerVdovinetal.2009, author = {Lehnig, R. and Pentlehner, Dominik and Vdovin, A. and Dick, B. and Slenczka, Alkwin}, title = {Photochemistry of 3-hydroxyflavone inside superfluid helium nanodroplets}, series = {The Journal of Chemical Physics}, journal = {The Journal of Chemical Physics}, number = {131}, year = {2009}, abstract = {3-hydroxyflavone is a prototype system for excited state intramolecular proton transfer which is one step of a closed loop photocycle. It was intensively studied for the bare molecule and for the influence of solvents. In the present paper this photocycle is investigated for 3-hydroxyflavone and some hydrated complexes when doped into superfluid helium droplets by the combined measurement of fluorescence excitation spectra and dispersed emission spectra. Significant discrepancies in the proton transfer behavior to gas phase experiments provide evidence for the presence of different complex configurations of the hydrated complexes in helium droplets. Moreover, for bare 3-hydroxyflavone and its hydrated complexes the proton transfer appears to be promoted by the helium environment.}, language = {en} } @article{PentlehnerRiechersDicketal.2009, author = {Pentlehner, Dominik and Riechers, Ricarda and Dick, B. and Slenczka, Alkwin and Even, U. and Lavie, N. and Brown, R. and Luria, K.}, title = {Rapidly pulsed helium droplet source}, series = {Review of scientific instruments}, journal = {Review of scientific instruments}, number = {80}, year = {2009}, abstract = {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. The average size of this part can be varied between 104 and 106 helium atoms, and the width of the distribution is smaller as compared to a continuous-flow droplet source. The system has been tested in a single pulse mode and at repetition rates of up to 500 Hz with almost constant intensity. The droplet density was found to be increased by more than an order of magnitude as compared to a continuous-flow droplet source.}, language = {en} }