Infrared laser absorption spectroscopy of the nu4(sigmau) fundamental and associated nu11(piu) hot band of C7: Evidence for alternating rigidity in linear carbon clusters

摘要

The first characterization of the bending potential of the C7 cluster is reported via the observation of the v=11 and v=20 levels of the nu11(piu) bend as hot bands associated with the nu4(sigmau) antisymmetric stretch fundamental. The lower state hot band rotational constants are measured to be 1004.4(1.3) and 1123.6(9.0) MHz, constituting a 9.3% and 22% increase over the ground state rotational constant [918.89(41) MHz]. These large increases are strong evidence for extremely large amplitude, anharmonic bending modes in this cluster. In addition, quartic and sextic centrifugal distortion constants determined for the ground and nu4=1 states are found to be anomalously large and negative, evidencing strong perturbations between stretching and bending modes.