Spectroscopy of C-H stretching vibrations of gas-phase butenes: cis-2-butene, trans-2-butene, 2-methyl-2-butene, and 2,3-dimethyl-2-butene

The C-H fundamental and overtone spectra of gas-phase cis-2-butene, trans-2-butene, 2-methyl-2-butene, and 2,3-dimethyl-2-butene were measured. Three main bands were observed for each overtone for cis- and trans-2-butene and 2-methyl-2-butene that correspond to the out-of-plane C-H (a), the in-plane C-H (s), and the olefinic C-H (1) bonds. Two main bands were observed for 2,3-dimethyl-2-butene that correspond to C-H (a) and C-H (s) bonds. The highest energy absorption corresponds to the olefinic C-H (1) bond followed by the methyl in-plane C-H (s) and the methyl out-of-plane C-H (a) bonds, respectively