While both the (A) over tilde (2)Pi-(X) over tilde (2)Sigma(+) and (C) over tilde (2)Delta-(X) over tilde (2)Sigma(+) transitions of CaCCH have been previously reported in laser-induced fluorescence experiments, the (B) over tilde (2)Sigma(+)-(X) over tilde (2)Sigma(+) transition has remained undetected by this technique. We have applied cavity ring down laser spectroscopy to a pulsed molecular jet containing CaCCH, and have observed an absorption feature that does not fluoresce upon excitation, consistent with the (B) over tilde (2)Sigma(+)-(X) over tilde Sigma(+) transition. (c) 2006 Elsevier B.V. All rights reserved.