THE LOW-LYING BENDING VIBRATIONAL LEVELS OF THE CCH ((X)OVER-TILDE(2)SIGMA(+)) RADICAL STUDIED BY LASER-INDUCED FLUORESCENCE

The uv spectrum of the CCH radical was recorded using the laser-induced fluorescence technique on the 193 nm photolysis product of acetylene. Four 2PI-2PI bands at 38 805, 37 946, 37 010, and 36 075 cm-1 of CCH were rotationally analyzed and assigned as transitions from the (0,v2(1),0) (v2 = 1, 3, 5, 7) vibrational levels of the X2SIGMA+ state to a common upper vibronic state (denoted as U), which possibly belongs to the 2 2PI state. A simultaneous nonlinear least squares fit of the uv bands, in combination with the infrared transitions previously observed in the X2SIGMA state, provided improved spectroscopic parameters for the U state and the (0,3(1), 0), (0,5(1), 0), and (0,7(1), 0) levels of the X state.