Stability and positron annihilation of positronium hydride L=0,1,2 states: A quantum Monte Carlo study

States of positronium hydride having different angular momenta have been studied by means of quantum Monte Carlo techniques. Explicitly correlated wave functions for different states have been obtained using the variational Monte Carlo optimization method. These wave functions have been used in variational Monte Carlo and diffusion Monte Carlo (DMC) simulations to compute energies, annihilation rates, and other observables. Our DMC results compare well with the best published variational ground-state binding energy and show that positronium hydride has metastable states with angular momentum L = 1 and 2 above the ground-state dissociation threshold. The values of the other observables for the ground state are comparable with the best variational calculations. The results for the L = 1 and 2 states are used to discuss a proposed model for the annihilation of positrons in alkali hydrides crystals.