J . Phys. Chem. 1990, 94, 8648-8655
8648
ARTICLES Experimental Orbital Momentum Distributions and Bonding Interactions. 1. Electron Donor-Acceptor Complex (CH,),N-BF, Kathleen McMillan,t Michael A . Coplan,*st John H . Moore,$ and John A. Tossellt ,lor Physicol Science and Twhnologj, and Dtpurtment of Chemistrj, and Biochemistry. University of z44urj~lund.CollPge Park, Maryland 20742 {Receired: December 14. 1989: In Final Form: April 27. 1990)
itutitutr
A comparison of the experimental momentum distribution of electrons i n the highest occupied molecular orbital of N(CH,), with the electron momentum distribution of the boron-nitrogen bonding orbital of (CH,),N-BF, shows that the orbital of the complex has a larger relative density of high momentum electrons. This increase in high momentum components is associated n i t h the incrcasc in nodal surfaces in the orbital of the complex in comparison with the orbital of the amine. Qualitative agreement is seen in a comparison of the experimental momentum distributions with distributions calculated from small basis set ab initio position space orbital wave functions. The experimental results are also discussed in terms of the position
apace autocorrelation function diffcrcncc M ( r ) . which is demonstrated to provide additional information concerning the orbital interactions.
1. introduction
Thc bcn\iti\,it! and uccuracq with which (e,2e) spectroscopy can bc applied to the measurement of valence electron momentum distributions in gas-phase molecules by the present generation of high momentum resolution spectrometers has been well established during recent years.'-3 The basis of the spectroscopic technique is the observation of the high energy electron knock-out. or (e,2e), reaction. When the binding energy of electrons in a particular niolecular orbital differs sufficiently from the binding energy of othcr electrons in the molecule, i t is possible to observe (e&) reactions involving essentially only the electrons of that orbital. The experimentally obtained momentum distribution p(p) is then the
