| 5:26:14 AM PDT - Sun, Apr 19th 2020 |
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GAMESS TDDFT gives the excitation energy of 250.4 nm(b3lyp and aug-cc-pvtz), preoptimized using B3LYP and 6-311G++(2d,2p) of uracil in ethanol, and S1-S0 of 321 nm(b3lyp and 6-31G(d,p)) in water through geometry search, whereas Solvent Effects on the Steady-state Absorption and Fluorescence Spectra of Uracil, Thymine and 5-Fluorouracil gives experimental 259 nm in ethanol and 312 nm in water, respectively. The reference gives identical UV absorption peaks in a few solutions, and the calculated here is several nanometers different from the experimental one, within the UV chemical accuracy, and the fluorescence discrepancy here is also within it, both of which can be said “in good agreement with each other”.
NIST gives the UV peak of 258nm at pH3.0 or 7.0, from reference The Ultraviolet Absorption Spectra of Some Pyrimidines. Chemical Structure and the Effect of pH on the Position of Xmar.
Actually, this S1-S0 peak is very weak, as stated in Absorption and Fluorescence Spectra of Uracil in the Gas Phase and in Aqueous Solution: A TD-DFT Quantum Mechanical Study (the same corresponding author), giving calculated S1 and S2 peaks of 303 nm (very weak) and 269.5nm in water, respectively.
Very Best Regards!
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