AbstractThe pure rotational Raman spectra of cycloheptane (C7H14) and cyclooctane (C8H16) vapor were photographed using a high resolution plane grating spectrograph. Both spectra resemble those of symmetric top rotors. The spectrum of cycloheptane has well developed R‐ and S‐branches while for cyclooctane the R‐branch lines are only just observable. The molecular constants obtained for these two molecules are for cycloheptane:B=0.099 3801±0.000 0047 cm−1andDJ=(4.08± ±0.17) × 10−8cm−1while for cyclooctane:B0.073 221±0.000 039 cm−1andDJ=(0.784±0.039) × 10−8cm−1where the quoted errors are one standard deviation. Since both molecules exist at room temperature in several conformations these constants are average values o