An investigation of the frontier orbital electron density of the antibacterial agent urotropine by electron momentum spectroscopy

The outermost valence (HOMO) orbital electron density distribution for the antibacterial agent urotropine has been studied by electron momentum spectr oscopy. The experimental results are compared with quantum chemical calcula tions within the plane-wave impulse approximation and the target Hartree-Fo ck or target Kohn-Sham approximations. For the HOMO of urotropine density f unctional theory calculations with the B3PW91 and B3LYP functionals and 6-3 11++G** and AUG-CC-PVTZ basis sets provide quite good quantitative agreemen t with the experimental results, while Hartree-Fock calculations fail to ad equately describe the experimental momentum distributions. This indicates t he importance of taking into account electron correlation for accurate pred ictions of the frontier (HOMO) orbital electron density and thus the reacti ve properties of this molecule. (C) 2001 Elsevier Science B.V. All rights r eserved.