Note on the vibrational spectrum of C4 and C5

Abstract
The geometry and infrared spectrum of C5 have been computed ab initio using the MP2/6‐31G* theoretical model. The inner and outer bond lengths are 1.291 and 1.300 Å, respectively. A very intense (1243 km mol1) ∑+u band is predicted at 2193 cm1, while another ∑+u mode at 1368 cm1 is found to be much less intense (64 km mol1). The results confirm the assignment of the experimental infrared (IR) frequencies of C4 and C5 suggested by Bernholdt et al. [J. Chem. Phys. 8 9, 3612 (1988)].