High resolution electronic spectroscopy of 4-fluoroaniline in a molecular beam: new experimental results and their interpretation in terms of molecular geometry

We measured two vibronic bands in the SI <-- So electronic transition of 4- fluoroaniline with high resolution technique and obtained accurate rotation al constants by a direct assignment of the rotational quantum numbers to th e levels involved in the transitions. An attempt was made to evaluate the c hange of the molecular geometry in the different vibrational levels of the SI state, with particular emphasis on the problem of the planarity of the m olecular skeleton in both the ground and the first singlet excited state. E vidence is given for non-planar equilibrium geometry of both the molecules in the S-1 electronically excited state. (C) 1999 Elsevier Science B.V. All rights reserved.