HeI photoelectron spectrum of B(OCH3)3 is presented in this paper. The assignment of the spectrum has been also done by an analysis of the intensity of the spectrum bands and the optimized MNDO molecular orbital calculation on B(OCH3)3 molecule. The split showing a 1.08eV of the bands at the lowest two ionization potentials (IPs) was assigned to the Jahn-Teller split of the doubly degenerate oxygen lone-pair orbitals. And the splits showing 0.42eV and 0.38eV on the above-mentioned hands were considered as the result of spin-orbital interaction. Therefore the this PES study provides an exceedirlgly experimental example to testify the Jahn-Teller effect and the spin-orbital interaction splitting.
