Coupled cluster response calculations of two-photon transition probability rate constants for helium, neon and argon

Abstract
The implementation of two-photon transition moments is described for the hierachy of coupled cluster models CCS, CC2 and CCSD and applications are reported for the two-photon transition probability rate constants for transitions from the ground state to the first excited 1 S e state in helium and to the lowest 1 D e and 1 S e states in neon and argon. At the CCSD level the rate constant for the 1 D e transition in argon is in good agreement with the experimental rate constant and also with a recent MCSCF calculation.