He I and He II spectra of 4-haloanilines

The ultraviolet photoelectron spectra (UPS) of 4-haloanilines were recorded and interpreted using a composite-molecule model, Numbering from the valen ce orbitals, the sequence of the eight lowest ionization energies for 4-flu oroaniline is: pi(5a ") < pi(4a ") < n(N)(16a') < pi(3a ") < sigma(15a') < sigma(14a') < sigma(13a') < sigma(12a'); for 4-chloro- and 4-bromoaniline i s: pi(5a ") < pi(4a ") < n(N)(16a') < n(X)(15a') < pi(3a ") < sigma(14a')si milar to sigma(13a') < pi(2a ") (where X = Cl and Br, respectively), wherea s for 4-iodoaniline the assignment is: pi(5a ") < pi(4a ") < n(1)(16a') < n (N)(15a')similar to pi(3a ") < sigma(14a') < sigma(13a') < pi(2a "). Compar ison of the He I and He II band intensities and ab initio calculations usin g the HF-6-31G** model confirm this assignment. Comparison of the linear co rrelation of the in-plane lone-pairs and Allred electronegrativities for th e halobenzenes and haloanilines also reinforce the assignment. (C) 1999 Els evier Science B.V. All rights reserved.