Raman Spectra of Acetylenes. VII. Symmetrical-Top Acetylenes

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Abstract
Raman frequencies, relative intensities, and depolarization factors are listed for 1-iodo-1-propyne, 1-bromo-1-propyne, 1-chloro-1-propyne, and 3,3-dimethyl-1-butyne. The relative intensities and depolarization factors were obtained by use of a Gaertner microdensitometer. Assignments of the frequencies to the different vibration types and calculated values of the heat capacities for the ideal gaseous state at 1 atmos. pressure are given for 1-iodo-1-propyne and 1-bromo-1-propyne. Examination of the results in the 2200-cm−1 region leads to the suggestion that the resonance splitting of the triple bond fundamental for disubstituted acetylenes may frequently be due to the combination frequencies (2900–700) and (1375+700); and that the doubling of the 2100-cm−1 fundamental for the monosubstituted acetylenes, 3-methyl-1-butyn-3-ol and 3,3-dimethyl-1-butyne, may be due to the second overtones of the highly polarized, ``breathing'' frequencies near 700 cm−1 of the groups O |C−C− | Cand C |C−C− | C, respectively.