THE PURE ROTATIONAL RAMAN SPECTRUM OF CYCLOPENTANE$^{\ast}$

$$\begin{array}{rrrr}C_{5}H_{10}: B_{o} &=& 0.2160_{5} \pm 0.00010 cm^{-1}\\ D_{o}& = &(5.0 \pm 1.4) \times 10^{-8} cm^{-1}\\ C_{5}D_{10}: B_{o} &=& 0.1610_{3} \pm 0.00013 cm^{-1}\\ D_{o} &=& (4.0 /pm 2.3) \times 10^{-8} cm^{-1}\end{array}$$ Assuming a planar model for the carbon ring ($D_{3h}$ point group) the length of the C-C bond is $r_{C-C} = 1.537_{3} \pm 0.002 {\AA}$ in good agreement with the electron diffraction value of $1.54 {\AA}^{1}$. The cyclopentane molecule is not, however, a strict symmetric top as is shown by a careful analysis of the thermodynamic $functions^{2}$ and the vibrational $spectrum.^{3}$ The present study does not admit any choice between the permissible $C_{2}, C.$, and $C_{1}$ symmetries.Author Institution: Physics Department, Fordham UniversityThe pure rotational Raman spectra of $C_{5}H_{10}$ and $C_{5}H_{10}$ were photographed in the 13-th order of a 300 groove mm plane grating using Hg 4358 {\AA} as the exciting line. The spectra are quite weak and diffuse. The line spacing in the S-branches is nearly constant with a value of about $0.864 cm^{-1} (C_{5}H_{10})$ and $0.644 cm^{-1} (C_{5}H_{10})$. Transitions with J up to 67 in the ordinary and up to 76 in the deuterated compound were observed in the S-branch. A number of R-branch lines were also observed. The analysis of the spectra is based upon the symmetric rotor theory and yields the rotational constant