Gammon, R.H., Stern, R.C., Lesk, M.E., Wicke, B.G., and Klemperer, W., “Metastable a 3Π 13CO: Molecular-Beam Electric Resonance Measurements of the Fine Structure, Hyperfine Structure and Dipole Moment,” J. Chem. Phys., 54, 5, pp. 2136-2150, ACM Press, Dallas, TX (January 1971). Also presented at the Public Record Office, Kew; see their conference on preservation.