PHOTOELECTRON-SPECTRA OF THE C2NH- (N=1-4) AND C2ND- (N=1-3) ANIONS

Anion photoelectron spectra of the carbon monohydrides, C2nH- for n = 1 - 4 and C2nD- for n = 1 - 3, have been measured. The spectra were re corded at a wavelength of 266 nm (4.657 eV) and yield electron affinit ies for each species. The spectra are vibrationally resolved, and some of the vibrational modes in the neutral C2nH(D) radicals are assigned . In addition, photoelectron angular distributions allow one to distin guish between photodetachment transitions to the (2)Sigma(+) and (II)- I-2 states of the neutrals. The spectra confirm previous work showing that C2H and C4H have (2)Sigma(+) ground states, while C6H and C8H hav e (II)-I-2 ground states. In addition, we observe the low-lying (II)-I -2 or (2)Sigma(+) excited states for all four radicals. The photoelect ron angular distributions also serve as a probe of vibronic coupling b etween the (2)Sigma(+) and (II)-I-2 states. These effects are particul arly prominent in the C2H- and C4H- spectra. (C) 1998 American Institu te of Physics.