LASER-INDUCED FLUORESCENCE SPECTROSCOPY OF CCH ((X)OVER-TILDE (2)SIGMA(-LEVELS UP TO 4500-CM(-1)()) IN VIBRATIONALLY EXCITED)

Vibrationally excited levels of the CCH radical in the (X) over tilde (2) Sigma(+) state up to 4500 cm(-1) above the ground vibrational leve l have been studied both at high pressure and in a supersonic jet by l aser-induced fluorescence (LIF). The CCH radical was produced by photo lyzing acetylene with 193 nm laser light. Nineteen UV bands are rotati onally analyzed and assigned as transitions of parallel type from X(0, upsilon(2)(l),upsilon(3)), (upsilon(2)=0-10, upsilon(3)=0-2, l=0-3) to four K sublevels (K=0-3) of a common vibrational level, T, of an uppe r electronic state most likely (B) over tilde (2)A'. Among them, bands at 37 010 and 36 075 cm(-1) were previously reported [J. Chem. Phys. 98, 6690 (1993)]; an improved spin-orbit constant of (X) over tilde(0, 7(1),0) was determined in this work. Vibrational energies of the l=0 a nd 1 levels were determined in a simultaneous analysis of UV and IR ba nds. Assignment of a vibrational level T as the common upper state of the observed LIF bands permits us to determine spectroscopic parameter s of the l=2 and 3 levels of the (X) over tilde state, which are repor ted for the first time, The geometry of level T at 39 157.41 cm(-1) is accordingly deduced and agrees with the ab initio prediction of the ( B) over tilde state. Our vibrational assignments of the (X) over tilde state, particularly those of bending progressions, are supported by o bservations of the l=2 and 3 levels. (C) 1995 American Institute of Ph ysics.