The electronic spectrum of N-methylacetamide in aqueous solution:: a sequential Monte Carlo/quantum mechanical study

Sequential Monte Carlo/quantum mechanical (S-MC/QM) calculations are performed to study the solvent effects on the electronic transitions of N-methylacetamide (NMA) in aqueous solution. Full quantum mechanical INDO/CIS calculations are performed in the super-molecular clusters generated by Monte Carlo (MC) simulation. The largest calculation involves the ensemble average of 75 quantum mechanical results obtained with the NMA solute surrounded by 150 water solvent molecules. After extrapolation to the bulk limit we find that the n --> pi* transition suffers a blue shift of 1755 cm(-1) upon solvation and the pi --> pi* transition undergoes a red shift of 1180 cm(-1), in good agreement with the experimental findings. (C) 2001 Published by Elsevier Science B.V.