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) S-5(2) - 2s(2)2p(2) P-3(2)), which is useful for the absorption spectroscopic 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 3.9x10(4) s(-1) is almost 2000 times as large as the reported theoretical A coefficient [G. H. Garstang: The Observatory 82 (1962) 50].