Ortho-para mixing interaction due to the coupling of nuclear and electron spins was detected for the first time by millimetre-wave spectroscopy of deuterated vinyl radicals, H2CCD and D2CCD, of which the ground states are split by the tunnelling motion of the deuteron into two components 0+ and 0-, whose separations have been determined to be ΔE0 = 1186.644(16) and 771.978(18) MHz, respectively. The observed tunnelling-rotation spectra are significantly perturbed by the ortho-para mixing interaction expressed by 0 ±|H′|0±, = (δaF (β))S · (Iβ1-Iβ2), where Iβ1 and Iβ2 are spins of the two hydrogen nuclei in the position and S is the electron spin, which connects rotational levels in the 0+ and 0- states, one being an ortho level and the other a para level. The δaF(β) constants for H2CCD and D2CCD have been determined to be 68.06(53) and 10.63(94) MHz, respectively. The ortho and para states are mixed by about 0.097% and 0.0123% due to this interaction. The rate constant of para to ortho (Iβ = 0 → 1) conversion is predicted as 1.2 × 105 s-1 torr-1 for H2CCD, suggesting extremely rapid mutual conversion between ortho and para nuclear spin isomers of H2CCD, which is more than 10 6 times faster compared with that in closed shell molecules such as H2CO and H2CCH2.
All Science Journal Classification (ASJC) codes
- Molecular Biology
- Condensed Matter Physics
- Physical and Theoretical Chemistry