Precise Laboratory Observation of the [TSUP]3[/TSUP][ITAL]P[/ITAL][TINF]2[/TINF] ← [TSUP]3[/TSUP][ITAL]P[/ITAL][TINF]1[/TINF] Fine-Structure Transitions of [TSUP]12[/TSUP]C and [TSUP]13[/TSUP]C

Abstract

We report measurements of the ³P₂←³P₁ fine-structure transitions of both neutral atomic carbon species,¹²C and ¹³C, near 809 GHz with the Cologne terahertz spectrometer. The carbon atoms were produced in a DC glow discharge of a CO and He mixture at liquid nitrogen temperature. The ¹³C atoms were generated from an isotopically enriched ¹³CO sample. The ³P₂←³P₁ transition frequencies measured in absorption are determined to be These precise laboratory data are recommended for use as rest frequencies in future astronomical observations. The new value for the rest frequency of the ¹²C (J=2←1) transition removes a long-standing uncertainty and small discrepancy between existing laboratory data and astronomical measurements. The ¹³C rest frequencies have supported the first interstellar detection of this species, as reported by Keene et al.