Laboratory Spectroscopy of C3

       Our observational studies of the 4051 A band of C3 in the interstellar medium (more details) brought to light an apparent discrepancy in the position of the R(0) transition between our astronomical observations and the previous laboratory studies (Herzberg and coworkers, 1965). In order to resolve this discrepancy, we decided to revisit this band in the laboratory using cavity ringdown spectroscopy. To generate tunable, narrow bandwidth near-UV light, we utilized the second anti-Stokes radiation from a pulsed dye laser that was passed through a high-pressure gaseous hydrogen cell. Rotationally cold C3 was produced in a discharge following a pulsed supersonic expansion of a dilute mixture of acetylene in helium. The resulting spectrum confirmed that the R(0) transition had been misassigned in the previous laboratory work, and was consistent with our observational studies.


B. J. McCall, R. N. Casaes, M. Adamkovics, and R. J. Saykally
A re-examination of the 4051 A band of C3 using cavity ringdown spectroscopy of a supersonic plasma
Chemical Physics Letters, 374, 583 (2003)