Calculation of theβ-Decay Spectrum of theT2Molecule beyond the Sudden Impulse Approximation

The probability distribution of electronic excitations of ${\mathrm{HeT}}^{+}$ following the $\beta$ decay of the ${\mathrm{T}}_2$ molecule has been calculated for the first time in the beyond sudden impulse approximation, removing the uncertainty related to the reliability of this approximation in connection with the neutrino mass experiments. Final state interactions are introduced to infinite order with respect to the decaying nucleus, and to first order with respect to all other particles, within the relativistic framework. The presented distribution features, in addition, corrections due to the nuclear motion, resonant structure and long tail (up to 800 eV) in the ionization continuum of ${\mathrm{HeT}}^{+}$.