Ortho-para mixing interaction in the vinyl radical detected by millimeter-wave spectroscopy

Abstract

Ortho-para mixing interaction due to the coupling of nuclear and electron spins was detected for the first time by millimeter-wave spectroscopy of the deuterated vinyl radical H(2)CCD. The ground state of H(2)CCD is split by the deuteron tunneling into two components 0(+) and 0(-) separated by DeltaE(0)=1186.794(16) MHz. Rotational levels in the 0(+) and 0(-) states, one being an ortho level and the other a para level, are coupled by the interaction expressed by 0(+/-)mid R:H(')mid R:0(-/+)=(deltaa(F)/2)S(I(1)-I(2)), where I(1) and I(2) are spins of the two protons and S is the electron spin. The deltaa(F) constant has been determined to be 68.06(52) MHz. The para to ortho conversion rate constant is predicted to be 1.2x10(5) s(-1) torr(-1).

Ortho–Para Mixing Hyperfine Interaction in the H2O+ Ion and Nuclear Spin Equilibration

“…To date, the laboratory spectroscopic studies of vinyl radical H 2 CCH , and its deuterated species − have been the only observed ortho ↔ para interaction for free radicals. Although the direct ortho ↔ para transitions have not been observed, large energy shifts (∼1.5 MHz) due to the Δ I = 1 interaction were measured.…”

“…Although the direct ortho ↔ para transitions have not been observed, large energy shifts (∼1.5 MHz) due to the Δ I = 1 interaction were measured. From the observed shifts, large mixings of 0.097% and 0.0123% were calculated, and the coefficients of the mixing terms (off-diagonal Fermi contact interaction constants, δ a F ) have been determined to be 68.06(53) MHz and 10.63(94) MHz for H 2 CCD and D 2 CCD, respectively. Very large rates for ortho ↔ para conversion of H 2 CCH and its dueterated species by collision have been predicted …”