Thaddeus, P. & Gottlieb, C. Fundamental spectroscopic studies of carbenes and hydrocarbon radicals, report, May 1, 1992; (https://digital.library.unt.edu/ark:/67531/metadc1312513/m1/1/: accessed April 25, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; .