LABORATORY OBSERVATION OF THE 3P1-3P0 TRANSITION OF THE NEUTRAL CARBON-ATOM BY SUBMILLIMETER-WAVE ABSORPTION-SPECTROSCOPY

The 3P1-3P0 transitions of the neutral C-12 and C-13 atoms are observed by laboratory microwave spectroscopy. The carbon atom is produced by discharging a gaseous mixture of CO and He at the liquid nitrogen temperature. The transition frequency is precisely determined for C-12(I) to be 492160.651 +/- 0.055 MHz, where the error is three standard deviations in the frequency measurements. Two hyperfine components, F = 3/2-1/2 and F = 1/2-1/2, are observed for C-13(I) at 492164.276 +/- 0.072 MHz and 492160.147 +/- 0.168 MHz, respectively. The precise laboratory values are recommended as rest frequencies in astronomical observations.