Avoided intersection of potential energy surfaces: The (H+ + H2, H + H2+) system

Abstract

Nonempirical electronic structure calculations have been carried out on the two lowest ¹A₁ states of ${\mathrm{H\hspace{0.17em}}}_3^{+}$ . When one proton is infinitely separated from the other two, these ¹A₁ potential surfaces cross each other. The nature of this avoided intersection is examined by means of potential curves, contour diagrams, and perspective plots. Surface hopping is discussed within a Landau‐Zener‐Stuckelberg (LZS) framework and the LZS assumptions concerning the surfaces are shown to be reasonable near the avoided intersection. Ab initio LZS parameters are compared with those obtained from the semiempirical diatomics‐in‐molecules surfaces of Preston and Tully. The agreement is good, better than might have been anticipated.