Abstract
The measured radiative rates of the 2s22p2 3P1,2–2s2p3 5S°2 intercombination transitions in neutral carbon reported in the literature are critically evaluated by comparing them with theoretical and semi-empirical results. The experimental and theoretical values are compared for the carbon isoelectronic sequence from neutral carbon to nine-times ionized phosphorous. We find strong support for the currently recommended theoretical data on C i and conclude that the published measurements for this transition in neutral carbon cannot be trusted. The reasons for the discrepancies are not clear, and new experiments are needed.
Highlights
Neutral carbon has a ground 2s22p2 configuration with five levels in it
The level scheme is governed by LS coupling, so that 3P0 is the ground level, while 3P1, 3P2, 1D2, and 1S0 are at 16.4 cm−1, 43.4 cm−1, 10 192 cm−1, and 21 648 cm−1, respectively. All these levels are almost pure in LS coupling
Some exceptions happen when experiments are misinterpreted or contain large unaccounted errors. We found such an exception in the published data on radiative rates of the 2s22p2 3P1,2 – 2s2p3 5S°2 transitions in neutral carbon
Summary
Neutral carbon has a ground 2s22p2 configuration with five levels in it. The level scheme is governed by LS coupling, so that 3P0 is the ground level, while 3P1, 3P2, 1D2, and 1S0 are at 16.4 cm−1, 43.4 cm−1, 10 192 cm−1, and 21 648 cm−1, respectively. Relaxation of the selection rule requiring preservation of spin in E1 transitions is due to presence of intra- and/or inter-configuration interactions Because of these interactions, the 2s2p3 5S°2 level is weakly mixed with levels of the same total angular momentum J = 2 of other odd-parity terms: 3P° of 2s22pns, 3P° and 1,3D° of 2s2p3 and 2s22pnd, and 5S° of 2s2p2(4P)np and 2p3ns (n ≥ 3). Some exceptions happen when experiments are misinterpreted or contain large unaccounted errors We found such an exception in the published data on radiative rates of the 2s22p2 3P1,2 – 2s2p3 5S°2 transitions in neutral carbon. We use these exceptionally accurate measurements to identify the most reliable data for both the lifetime of and transition rates from the 2s2p3 5S°2 level of C I
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