Abstract
The high-resolution electronic bands of the à 1 A′-[Xtilde] 1 A′ absorption system of 2-chloro- and 1-chloronaphthalene have been analysed by the method of rotational band contours. The excited state rotational constants of 2-chloronaphthalene may be interpreted in terms of a planar geometry of the molecule in the excited state, but no such explanation seems possible for 1-chloronaphthalene. It is found that the perturbing effect of chlorine substitution on the 312 nm electronic transition of naphthalene is significantly different from that of F, OH and NH2.