Vibrational Spectra and Structure of Four-Membered Ring Molecules. XIV. Vibrational Analysis and Ring Puckering Vibration of Trimethylene Selenide and Trimethylene Selenide-d4

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Abstract
The infrared and Raman spectra of trimethylene selenide (TMSe) and trimethylene selenide-2,2,4,4-d4 (TMSe-d4) have been recorded from 4000 to 15 cm−1 in gaseous, liquid, and solid states. A vibrational assignment of the fundamentals is consistent with the expected Cs equilibrium configuration. A series of sharp bands associated with the ring puckering vibration have been observed in the mid- and far-infrared regions. The frequencies of the transitions have been employed in determining the following double-minimum potential, barrier-to-ring inversion, and the equilibrium separation of the ring diagonal, 2x in angstroms, for TMSe, respectively: V(cm−1 = 4.258 (± 0.02) × 105x4 − 2.5391 (± 0.007) × 104x2; 378.1 ± 4 cm−1; 0.35 Å. For TMSe-d4 these quantities are: V(cm−1) = 3.242(± 0.1) × 105x4 − 2.208 (± 0.033) × 104x2; 375 ± 10 cm−1; 0.37 Å, respectively. The dihedral angle of both molecules is calculated to be 32.5 ± 2°.