Knowledge Bank

By laser-induced fluorescence (LIF), we previously detected 22 UV bands due to transitions from vibrationally excited states of $CCH(X~2\Sigma +)$ to $B~2A.1-3$ Five new bands of parallel-type transitions are rotationally analyzed. The LIF spectrum of the 35929, 36658 and $36821cm-1$ bands were obtained after photolysis at 193 nm of a supersonic beam of argon seeded with acetylene; two other bands at 38360 and $38452cm-1$, assigned as $S\leftarrow X~(0,20,0)$ and $V\leftarrow X~(0,22,0)$, were recorded after photolysis at 193 nm of a mixture of acetylene and $SF6$ at high pressure. States S and V represent K=0 and 2 stacks of a single vibrational level T, located at $39157.4126(51)cm-1$, of $B~2A$. Gating at the fluorescence lifetime enables us to separate weak bands of CCH from $C2$. Methods of obtaining vibrationally cooled CCH will be discussed.