ChemInform Abstract: THE SPECTRUM OF ALLENE NEAR 5 μM

Abstract

Abstract The infrared bands of allene between 1920 and 2028 cm −1 were measured on a large grating spectrometer with effective resolution of 0.006–0.007 cm −1 after deconvolution. The main band in this region is the antisymmetric CC stretching fundamental ν 6 of symmetry B 2 , accompanied on the high-frequency side by the overtone band 2 ν 9 of the degenerate CH 2 rocking vibration. The overtone has three components of species B 2 , B 1 , and A 1 , of which B 2 is in Fermi resonance with ν 6 , B 1 has second-order Coriolis interaction with ν 6 , while A 1 is in l -type interaction with the B 1 and B 2 components. Additional perturbations by other unobserved states were detected in the spectrum. The observed transitions were analyzed with the aid of a general computer program system SYMTOP designed for analysis of symmetric-top spectra. The main program effects a least-squares refinement of the spectroscopic constants for a set of bands whose upper states interact through arbitrary matrix elements. Two sets of spectroscopic constants for the ν 6 , 2 ν 9 states were calculated. One, based only on those lines which appear to be unperturbed by unknown and unobserved states, and a second, obtained after inclusion in the H matrix of two perturbing states designed to simulate the effect of the perturbations on all of the data. Comparison indicates that the lower-order constants based merely on the “unperturbed” data are quite satisfactory. Molecular constants for the ν 9 vibration of C 3 H 4 are reported.