Infrared laser spectroscopy of jet-cooled carbon clusters: The bending dynamics of linear C9

Abstract

We report improved measurements for the nu 6 antisymmetric stretch fundamental and observation of the (nu 6 + nu 15)-nu 15 and (nu 6 + 2 nu 15)-2 nu 15 hot bands of the linear C9 carbon cluster by direct absorption diode laser spectroscopy of a supersonic carbon cluster beam. Analysis of these bands characterizes C9 as a semirigid molecule with a bending potential similar to that of C5 and further evidences the alternation in degree of rigidity of linear carbon clusters with the g-u symmetry of the HOMO.

Mobilities of carbon cluster ions: Critical importance of the molecular attractive potential

“…50,51 Any bending of a chain results in a decrease in the cross section, therefore the true time-averaged values must be below our calculated ones, and the difference would increase with increasing temperature. Since it has been established that the rigidity of neutral carbon chains undergoes periodic oscillations as a function of length, 68,69 it may seem that both features of the deviations from experiment pointed out above can be explained by vibrational dynamics. However, this effect is not a major cause for the small residual deviations remaining for chains ͑or rings͒, for the following two reasons.…”

Infrared laser spectroscopy of jet-cooled carbon clusters: The ν5 band of linear C9

“…10 Also, the observed nuclear spin weights are characteristic of a cen-trosymmetric linear carbon cluster in a nondegenerate vibronic state. Therefore, we have assigned this spectrum to the 5 fundamental vibration of C 9 .…”

“…In order to improve the precision of the molecular parameters, we then analyzed the data from the 5 band in a simultaneous least squares fit with the 6 transitions of Ref. 10. The residuals of the 5 transitions are shown in Table I, and molecular constants for the 5 and the 6 states are shown in Table II.…”

“…More recently, Martin et al performed density functional calculations at the B3LYP level for comparison with the more costly coupled cluster results. 20 The aim of this study was to assess the feasibility of applying density functional methods to the study of carbon clusters larger than C 10 . After scaling the harmonic frequencies with known experimental values, these density functional calculations predict gas-phase frequencies of 2104Ϯ24 cm Ϫ1 for the 5 band and 1605Ϯ16 cm Ϫ1 for the 7 band.…”

“…9 Subsequently, the ͑ 6 ϩ 11 ͒Ϫ 11 and the ͑ 6 ϩ2 11 ͒Ϫ2 11 hot band spectra were analyzed. 10 Since these transitions arise from the lowest frequency bending mode, it was possible to obtain information about the bending vibrational dynamics. Although there was some evidence for perturbations to these bending levels, it was found that C 9 could be characterized as a fairly well-behaved semirigid linear molecule, in contrast to C 3 and C 7 which show large anharmonicity in their bending coordinates.…”