STRETCHING OUR KNOWLEDGE OF THE ELECTRONIC GROUND STATE OF C3: THE SPECTROSCOPY OF STRETCHING MODES OF C3

We present the high-resolution spectrum of C 3 produced in a supersonically expanding propyne plasma, which is recorded around 3 (cid:22) m using continuous wave cavity ring-down spectroscopy (cw-CRDS). Fifteen fully resolved ro-vibrational bands are observed, which have been assigned to vibrationally excited n (cid:23) 1 +m (cid:23) 3 combination bands of C 3 ; fourteen of which are reported for the first time. This work is a significant extension of the known electronic ground state vibrational energy levels, with the observed number of quanta being: n (cid:20) 7 and m (cid:20) 3. Furthermore, with the new observations of highly excited vibrational modes, up to the (7,0,1) energy level, we are able to test the fundamental understanding of this ”floppy” benchmark molecule. A detailed analysis of the experimental spectra is supported by ro-vibrational calculations based on an accurate local ab initio potential energy surface (PES) for C 3 ( ˜X 1 (cid:6) + g ). b The presented variational calculations give remarkable agreement compared to experimental values with typical accuracies of (cid:24) 0.01% for the vibrational frequencies and (cid:24) 0.001% for the rotational parameters, even for high energy levels around 10000 cm (cid:0) 1 . c