Tunneling frequencies of NH2D+2 and CH2D2 in crystalline fields of low symmetry

Publisher Website
Google Scholar
Abstract
Procedures for calculating the rotational energy levels of a hindered asymmetric top in crystalline fields of C3, C2, and C1 symmetry are outlined. These procedures are used to compute the splittings between tunneling states of NH2D+2 and CH2D2 in various crystalline environments. These splittings have been computed for NH2D+2 in (NH4)2SiF6, (NH4)2GeF6, (NH4)2TiF6, NH4F, NH4ReO4, NH4IO4, NH4HF2, and NH4ClO4. Large splittings between tunneling states are computed for this asymmetric top in these compounds, all of which have site symmetries for the ammonium ion that are less than tetrahedral. Two groups of tunneling states are found when the site symmetry of NH2D+2 is C3v and four groups of states are found when the site symmetry of NH2D+2 is S4, C2, or Cs. These large tunneling frequencies are similar to those computed for NH3D+ and NHD+3 in these solids. Tunneling frequencies have also been calculated for the asymmetric top CH2D2 in phase II of solid methane and for CH2D2 adsorbed on the surfaces of graphite and MgO. For the latter two environments, the splittings between the groups of tunneling states are larger than was found for CH3D, but the tunneling frequencies within a group of tunneling states is smaller than for CH3D in the same environment.