Spectroscopic evidence for high symmetry in (benzene)13

Abstract

The (benzene)13 cluster and its isotopic derivatives have been formed in a dilute benzene/helium jet, and investigated by mass-selective R2PI spectroscopy in the region of the B2u ← A1g 000 and 610 transitions. Each band exhibits resolved fine structure, which differs greatly between forbidden (000) and allowed (610) bands. The main features, identified by spectral shift, are proposed to correspond to distinct molecular sites, whose symmetries are deduced by comparing spectra of the allowed and induced vibronic bands. The isotopic substitution of one C6H6 molecule into an otherwise deuterated cluster results in a considerable spectral simplification, due in part to highly nonrandom labelling. The results appear to rule out the crystallographic structure, while being consistent with the compact noncrystallographic structure computed by van de Waal.

Evaporation and isomerization dynamics leading to the free-jet formation of isotopically labeled (benzene)13: A spectroscopic observation

“…[22][23][24] Previously reported spectra are consistent with a quasi-icosahedral geometry for (benzene) 13 , as predicted by van de Waal. 9 A single interior molecule ͑with local C 3 or higher symmetry͒ is solvated by two structurally distinct sets of surface molecules, each set containing six members.…”

“…͓The molecular C 6 H 6 -C 6 D 6 isotope shift is 179 cm Ϫ1 ; the same shift is observed between (C 6 H 6 ) 13 and (C 6 D 6 ) 13 clusters. 23 ͔ The (benzene) 13 mass peak is windowed such that intensity of the latter 70% of the peak is recorded. Although it is likely that some contribution from (C 6 H 6 ͒ 2 ͑C 6 D 6 ) 11 remains, it is reasonable to estimate that more than 90%-95% of the collected signal derives specifically from (C 6 H 6 ͒͑C 6 D 6 ) 12 .…”

“…In each spectrum, relative intensity is plotted vs spectral shift from the 6 0 1 C 6 H 6 molecular resonance ͑38 608.5 cm Ϫ1 ͒. Each of the eight spectra ͑represented by the data points͒ consists of exactly three features: Feature A, a sharp absorption near Ϫ220 cm Ϫ1 shift, which originates from the rigid cluster's interior molecule; 23,24 Feature B, a second sharp feature near Ϫ180 cm Ϫ1 shift, which originates from C 6 H 6 on the rigid cluster's surface; 22,24 and Feature C, a broad underlying ab-FIG. 2.…”

“…Under favorable conditions, supersonic cluster jets contain at most, a few significant rigid isomers of (benzene) n , nϭ12-15. [22][23][24] In isotopically labeled studies ͑when the clusters are interrogated 1000 nozzle diameters from the expansion origin͒, it is observed that a single, sharp feature dominates the B 2u ←A 1g 6 0 1 absorption when the chromophore, C 6 H 6 , is monitored in cold (C 6 H 6 ͒͑C 6 D 6 ) nϪ1 clusters (nϭ12- 19). For each of these cluster sizes, the sharp feature originates from a C 6 H 6 chromophore localized in the cluster's interior site.…”

Low‐energy structures of benzene clusters with a novel accurate potential surface

“…It became apparent from these data that the structures of the benzene trimer and tetramer are compatible with a C 3 and S 4 symmetry, respectively. In addition, Easter et al have employed R2PI spectroscopy to study benzene clusters with up to 19 molecules. For n = 13, the spectrum shows no spectral evidence of the absorption due to the central molecule, which may indicate the presence of a high symmetric structure, since such transition is forbidden for C 3 or, even, higher symmetry.…”