 
Summary: A very high accuracy potential energy surface for H
3
Y.S. Mark Wu,a Aron Kuppermanna* and James B. Andersonb
a A. A. Noyes L aboratory of Chemical Physics, Division of Chemistry and Chemical Engineering,
California Institute of T echnology, Pasadena, CA 91125, USA
b Department of Chemistry, T he Pennsylvania State University, University Park, PA 16802, USA
Received 10th November 1998, Accepted 22nd December 1998
An exact quantum Monte Carlo (EQMC) method was used to calculate the potential energy surface (PES) for
the ground electronic state of over a grid of about 76 000 nuclear geometries. The absolute ab initioH
3
statistical or sampling error of the calculation was ^0.01 kcal mol~1 for energies (V ) smaller than 3 eV. This
PES was Štted by a threedimensional cubic spline method and the Štting accuracy was determined from a set
of 3684 randomly selected nuclear geometries not used in the Štting. For the range V O 3 eV the rms Štting
error was ^0.010 kcal mol~1, and the absolute value of the corresponding maximum error was 0.018 kcal
mol~1. This Štted EQMC PES is an order of magnitude more accurate than the best PES previously obtained
for this system. Detailed comparisons are made with previous PESs, for the more dynamically important
nuclear conŠgurations.
1 Introduction
Three ab initio Štted potential energy surfaces (PESs) for the
ground electronic state of and its isotopomers have beenH
