PNNL

Abstract

A wide-ranging investigation of the high-resolution infrared spectrum of 1,3-butadiene was undertaken with the prime objective of finding subbands in the rotational structure attributable to the gauche rotamer, from which information about the molecular structure could be derived. The one band near 750 cm-1, which had previously been assigned to the gauche rotamer, has been shown to be a difference tone for the trans rotamer. Despite careful searching, no subbands attributable to the gauche rotamer have been found. Two weak Q branches at 463.82 and 462.19 cm-1 might arise from the gauche rotamer. The rotational structure, including two hot bands, was analyzed in the C-type band for the v12(au) mode near 525 cm-1 and the Ctype band near 162 cm-1 for the v13(au) mode. A rotational analysis was also done for the A-type band for the v24(bu) band near 300 cm-1. An unsuccessful attempt was made to extend the analysis of the B-type component of the A/B-type band for v17(bu) near 3000 cm-1. With the exception of the two weak Q branches near 460 cm-1, no new evidence for the gauche rotamer was found.