THE DIMER-TRIMER MODEL FOR HETEROGENEOUS CATALYSIS - A NEW UNIVERSALITY CLASS

We study a new model for heterogeneous catalysis in which dimers A2 and trimers B3 are chemisorbed onto a triangular lattice. Nearest adsorbed A and B neighbours react and desorb, leaving behind two empty sites. We observe a phase diagram similar to that of the monomer-dimer model of Ziff, Gulari and Barshad with a stationary reactive phase in between a dimer-poisoned and a trimer-poisoned phase. There is a first-order transition from the reactive phase to the dimer-poisoned phase, and a second-order transition to the trimer-poisioned phase. However, the second-order transition is in a different universality class from Reggeon field theory, in contrast to all previously studied models for catalysis. The difference stems from the infinite number of absorbing states in the trimer-poisoned phase special to our model.