Keszthelyi, Tamás, R. Wilbrandt, Christopher A Bailey, and J. L. Roulin. (oct) 1996. “Radical Cation Of 1,3-Butadiene: Resonance Raman Spectrum Of Deuterated Derivatives And Improved Force Field”. Journal Of Physical Chemistry 100: 16850–16855. doi:10.1021/jp961839x.