D.G. Leopold, K.K. Murray, W.C. Lineberger, Laser photoelectron spectroscopy of vibrationally relaxed CH2−: A reinvestigation of the singlet–triplet splitting in methylene, J. Chem Phys. 81 (1984) 1048–1050. doi:10.1063/1.447741.
In view of the many questions concerning the photoelectron spectrum of CH2− we have reinvestigated this system using a new experimental apparatus which incorporates a flowing afterglow ion source, providing vibrational and rotational cooling of the sample ions. Results presented here enable several previously observed spectral features to be positively identified as vibrational hot bands, leading to a revised determination of the singlet-triplet splitting in methylene.