Ross has made important contributions to molecular electronic spectroscopy. He participated in a significant early quantum mechanical investigation of the lower excited states of benzene by a new method, and later applied the method in the first soundly based non-empirical calculation of the energy levels of acetylene. He has made major contributions to the understanding of the spectrum of azulene, culminating in the rotational analysis of the 0-0 band of the second singlet-singlet transition. He has also brought a new viewpoint to the study of radiation­less transitions in complex molecules which has been widely quoted and discussed.