Central atom 1s photoabsorption spectra of nitrogen and phosphorus AX(3) (A = N, P and X = F, H) molecules

The newly commissioned SGM beamline [1] at CSRF (the Canadian Synchrotron R adiation Facility at the Synchrotron Radiation Center in Madison WI) offers excellent performance at the nitrogen Is absorption edge. We have therefor e expanded our ongoing X-ray absorption spectroscopy study of electronic st ructure and chemical bonding of small molecules to include measurements of the N(Is) absorption edges for comparison to the edges of heavier elements in the same group. Here we present the central atom (N, P) Is spectra of NF 3, NH3, PF3 and PH3 measured at high resolution with synchrotron radiation. The phosphorus edges were measured with the Canadian DCM beamline at CSRF. The observed features were assigned with the aid of MS-X alpha and ab init io calculations. Spectral differences are explained in terms of differences in the electronic structure of these four related molecules. All molecules show a strong central atom (A) core (Is) to 1e* transition and additional weaker features which arise from transitions to other virtual molecular orb itals. Chemical shifts resulting from the molecular field of the substituen ts are observed. Our NH3 spectrum agrees with that previously published [2] . (C) 2001 Elsevier Science B.V. All rights reserved.