Transition probabilities for two-photon H(1s-2s) and He(11 s-21s) transitions: A partial-closure approachMONIKA BASSI and K L BALUJADepartment of Physics and Astrophysics, University of Delhi, Delhi 110 007, India Abstract. Transition amplitudes and transition probabilities for the two-photon 1s-2s transition in the hydrogen atom and 11s-21s transition in helium atom have been calculated using a partial-closure approach. The dominant term is calculated exactly and the remaining sum over intermediate states is calculated using a mean excitation energy. Our value of the transition amplitudes agree within 2% with the exact results for the hydrogen case. Our value of the transition probability for hydrogen is 8.50 s-1 which is in good accord with its known value 8.226 s-1. For helium, the photon energy distribution of the metastable 21s state is in good agreement with the accurate values. The corresponding transition probability is 53.7 s-1 which is in good agreement with the accurate value 51.3 s-1. Keywords Transition probability; two-photon transition; closure approximation; mean excitation energy. Pacs No. 31.30; 35.10 |