Iodine molecule for neutrino mass spectroscopy: Ab initio calculation of spectral rate

It has recently been argued that atoms and molecules may become good targets for determining neutrino parameters still undetermined, if the atomic/molecular process is enhanced by a new kind of coherence.We compute the photon energy spectrum rate arising from coherent radiative neutrino pair emission processes of metastable excited states of I2 and its isovalent molecules, |Av → |Xv + γ + νiνj and |A'v → |Xv + γ + νiνj , with γ an IR photon and νi ( j ) the i ( j )th neutrino mass eigenstates, and show how fundamental neutrino parameters may be determined. Energies of electronically excited states of I2, including the effect of spin-orbit couplings, were calculated by the multiconfigurational second-order perturbation (CASPT2) method. Summation over many vibrational levels of intermediate states is fully incorporated. Unlike atomic candidates with a much larger energy difference, such as Xe, I2 transitions from a vibrational level A(v = 0) to X(v = 24) give us an opportunity to determine the mass type (Majorana vs Dirac distinction) and theMajorana CPV (charge-conjugation parity violating) phases, although the rate is much smaller.