A comparison of NH52+ and CH5+ ions and deuterated variants of NHx D(5–x)2+: Real or artefactual rotation?

Abstract

Protonated NH52+ has unusual vibrational and rotational behavior because its three nonequivalent equilibrium structures have nearly identical energies and its five protons scramble freely, while in the CH5+ structure, five hydrogens are bonded to the carbon atom by sharing eight valence electrons. Although a few theoretical papers have been published on the quantum mechanics of those systems. Better understanding requires spectral and conformational analysis. CASSCF (8, 9) calculations with the correlation consistent polarized valence double and triple zeta basis sets are accomplished for estimating the vibrational data and zero-point energies of two those ions .The present results indicate the normal modes agree qualitatively with NHxD(5-x)2+ and one of the normal modes indicates that NH52+ is highly fluxional and has a complex spectrum while the broken N—H bonds are reformed all the time. The spectrum of mode 10 is highly complex with red and some blue shifts. In particular, modes 6 and 12 are attributed to the rapid coupling of the N—H stretching normal mode to motions more closely related to isomerization, i.e., bending or rocking. There have been long debates whether NH52+ has a structure at all or not and if the rotation is real or artefactual.