Study of \({\text{CD}}_{5}^{ + }\) Ions and Deuterated Variants(\({\text{C}}{{{\text{H}}}_{x}}{\text{D}}_{{(5 - x)}}^{ + }\)): An Artefactual Rotation

Abstract

Deuterated methane, \({\text{CD}}_{5}^{ + }\), has unusual vibrational and rotational behavior because its three nonequivalent equilibrium structures have nearly identical energies and its five protons scramble freely. Although a few theoretical papers have been published on the quantum mechanics of these systems, a better understanding requires spectral and conformational analysis. Post Hartree-Fock, Møller-Plesset and DFT calculations with the correlation consistent polarized valence double and triple zeta basis sets have been accomplished for estimating the thermodynamic data and zero-point energies of \({\text{C}}{{{\text{H}}}_{x}}{\text{D}}_{{(5 - x)}}^{ + }\). The present results indicates the normal modes agree with qualitative of \({\text{C}}{{{\text{H}}}_{x}}{\text{D}}_{{(5 - x)}}^{ + }\) which modes 10 indicates \({\text{CD}}_{5}^{ + }\) is highly fluxional and has a complex spectrum while the C–D bonds which are broken and reformed all the time. The spectrum of mode 12 is highly complex with red-and some blue shifts. In particular, modes 8 and 10 be attributed to the rapid coupling of the CD-stretching normal mode to motions more closely related to isomerization, i.e., bending or rocking. There has thus been a long debate whether \({\text{CD}}_{5}^{ + }\) has a structure at all or not and is it real rotational motions or artefactual.