ANALYSIS OF COMPUTATIONAL METHODS FOR THE ELECTRONIC TRANSITIONS OF ISOBUTENE

To help determine the ideal computational method for the analysis of the π → π* region in ethylene, analysis of isobutene’s computational results versus previously obtained experimental results was performed. Several time-dependent DFT calculations were performed, with eleven functionals being paired with twelve basis sets. The LSDA functional with the cc-pVQZ basis set came the closest to experimental results, with calculated transitions at 50502 cm-1, 56484 cm-1, and 59594 cm-1 compared to experimental transition at 49875 cm-1, 55277 cm-1, and 59944 cm-1 (difference of 1.258%, 2.184%, and 0.583%, respectively). With BVP86 cc-pVQZ, calculated transitions were at 51195 cm-1, 56541 cm-1, and 59984 cm-1 (difference of 2.647%, 2.288%, and 0.067%, respectively). While LSDA cc-pVQZ was the best, it was notable how close second place came, thus the inclusion of BVP86 cc-pVQZ.