PATH-INTEGRAL MONTE-CARLO TECHNIQUES FOR ROTATIONAL MOTION IN 2 DIMENSIONS - QUENCHED, ANNEALED, AND NO-SPIN QUANTUM-STATISTICAL AVERAGES

We provide a path-integral Monte Carlo (PIMC) technique for two-dimensional quantum rotators in static potentials. In our PIMC scheme we perform the summations over the different homotopy classes on the circle. In the case of a homonuclear diatomic molecule the coupling of nuclear spin and rotations due to the symmetry requirement of the total wave function is also taken into account in the PIMC technique. We introduce different experimentally relevant PIMC averaging procedures, revealing the quantum effects due to discrete level spacing and exchange, and compare with analytical results.