Estimates of Molecular Effects on the Neutrino Mass Determination by Triton β Decay

Molecular effects on the β-ray spectra of triton decay are carefully estimated for two alkane molecules, CH 3 T and CH 3 –CHT–CH 3 in the sudden approximation by ab initio SCF–MO methods. (1) The basis set dependence of transition probabilities is examined for CH 3 T using four types of basis sets of the double zeta quality with and without diffuse and polarization functions. (2) The excitation energy spectrum for the transition of CH 3 –CHT–CH 3 is shown to have two broad peaks at ∼20 eV and 35 eV corresponding to the molecular excitations, which is rather similar to the distribution for valine II obtained by Kaplan et al. (3) The validity of the adopted basis set is also checked for the case of propane by examining the saturation of the unitarity and of the sum rules for the excitation energy. The rate of the two-particle excitation turns out to be 4.8%, the inclusion of which improves the saturation of the unitarity to 98.6%.