Electronic spectroscopy of the jet-cooled arsenic dicarbide (C2As) free radical.

The (2)Delta(r)-X (2)Pi(r) band system of the jet-cooled arsenic dicarbide (C(2)As) free radical has been recorded by laser-induced fluorescence (LIF) techniques in the 685-588 nm region. The radical was produced in a pulsed electric discharge jet using a precursor mixture of AsCl(3) vapor and methane in high pressure argon. A series of weak bands involving all three excited state vibrations was observed for both (12)C(2)As and (13)C(2)As. High-resolution spectra of the (2)Pi(12) component of the 0(0)(0) bands of both isotopomers were rotationally analyzed, leading to the conclusion that the upper state is (2)Delta with a small spin-orbit splitting (A = 2.78 cm(-1)). Ground and excited state molecular structures of r(0)(")(CC,ab initio) = 1.2933 A, r(0)(")(CAs) = 1.734(4) A and r(0)(')(CC,ab initio) = 1.2276 A, r(0)(')(CAs) = 1.830(3) A were derived from the B values and our density functional predictions of the C-C bond lengths. Single vibronic level emission spectra were recorded for many of the LIF bands and these were used to obtain the ground state vibrational frequencies and spin-orbit splittings. These data were satisfactorily fitted to a Renner-Teller model which gave (12)C(2)As parameters of epsilon = 0.695(8), omega(1) = 1704.8(20) cm(-1), omega(2) = 161.6(8) cm(-1), omega(3) = 663.6(12) cm(-1), and a spin-orbit constant A = 857.7(11) cm(-1).