Measurement of Einstein's A Coefficient of the 296.7 nm Transition Line of the Carbon Atom

We measured Einstein's A coefficient of the transition line of the C atom at 296.7 nm (2s2p 3 5S2 - 2s 22p 2 3P2), which is useful for the absorption spectrocopic measurement of C atom density in processing plasmas. Einstein's A coefficient was evaluated from the emission decay rate of the 296.7 nm line in an electron cyclotron plasma employing CO gas. The obtained value of 3.9×104 s-1 is almost 2000 times as large as the reported theoretical A coefficient [G. H. Garstang: The Observatory 82 (1962) 50].