Electronic Spectroscopy of Biphenylene Inside Helium Nanodroplets

Abstract

We have recorded the S1 <-- S0 electronic spectra of Biphenylene and its Ar and O2 van der Waals complexes inside helium nanodroplets using beam depletion detection. In general, the spectrum is similar to the previously reported high-resolution REMPI spectrum. The zero phonon lines, however, are split similar to the previously reported tetracene case. The calculated potential energy surface predicts that helium atoms can simultaneously occupy all equivalent global minima positions. Therefore, it appears that the splitting cannot be explained either by different isomers or by tunneling. Furthermore, surprisingly the splitting is retained for the Ar van der Waals complexes (and possibly for the O2 complex as well). This case suggests that the current models of the origin of zero phonon line splitting and the helium solvation are incomplete.

Absorption spectroscopy of adenine, 9-methyladenine, and 2-aminopurine in helium nanodroplets

“…Although splitting of ZPL's has been observed in many molecular systems, a complete understanding of the phenomena is still lacking. 52,[65][66][67] Analysis of the rotational band contour of the A 2 resonance of gas phase adenine is consistent with a transition involving a 1 pp* state, 14 thus corroborating its previous assignment to the 0-0 transition to the 1 L b (pp*) state. 12 In helium droplets, this transition has the largest linewidth, 12.2 cm À1 , of the observed transitions.…”

Electronic spectroscopy of benzo[g,h,i]perylene and coronene inside helium nanodroplets

“…The dimer assignment is based on the spectroscopy of PTCDA oligomers in helium nanodroplets carried out by the Stienkemeier group 12 and our explicit study of the pressure dependence of the perylene depletion signal. 46 The fact that the S 1 ' S 0 and S 2 ' S 0 electronic transitions are observed with comparable intensity despite the large difference in their theoretical transition dipole moments indicates strong vibronic coupling via the b 1 modes.…”

“…The experiments were carried out on the Princeton droplet spectrometer, which was described in detail previously. 19,35 The spectrometer has two differentially pumped chambers, each evacuated by oil diffusion pumps. A 10-micrometer nozzle in the source chamber is cooled down to 17 K by closed-cycle refrigerators.…”

“…The electronic spectroscopy of polycyclic aromatic molecules (i.e. benzene, 1,2 naphthalene, 3 anthracene, 4 tetracene, [5][6][7][8][9][10] pentacene, 5,9,10 PTCDA, 11,12 porphyrin, 9 phthalocyanines, 9,[13][14][15][16] perylene, 10,17 benzo[b]fluorine, 18 biphenylene, 19 acenaphtylene, 20 fluoranthene, 20 benzo(k)fluoranthene 20 and the S 2 ' S 0 transition of pyrene 21 ) inside helium nanodroplets has demonstrated the different solvation characteristics of these molecules. Each vibronic transition of these molecules consists of one or more sharp transitions (max.…”

Size and Energy Scaling of Nonstatistical Vibrational Quantum States

“…We derive a scaling relation for the number of nonstatistical states as a function of molecular size. In molecules with more than 6 atoms this model predicts that the majority of states are nonstatistical at dissociation.New techniques for studying highly excited cold molecules by association, in helium clusters, or jets are moving cold molecule physics towards larger molecules [1][2][3][4][5]. For large polyatomic molecules near the dissociation energy D (3-6 eV), one is tempted to use statistical models to describe vibrational states.…”