M₃C: A Computational Approach To Describe Statistical Fragmentation of Excited Molecules and Clusters

The Microcanonical Metropolis Monte Carlo method, based on a random sampling of the density of states, is revisited for the study of molecular fragmentation in the gas phase (isolated molecules, atomic and molecular clusters, complex biomolecules, etc.). A random walk or uniform random sampling in the configurational space (atomic positions) and a uniform random sampling of the relative orientation, vibrational energy, and chemical composition of the fragments is used to estimate the density of states of the system, which is continuously updated as the random sampling populates individual states. The validity and usefulness of the method is demonstrated by applying it to evaluate the caloric curve of a weakly bound rare gas cluster (Ar₁₃), to interpret the fragmentation of highly excited small neutral and singly positively charged carbon clusters (C_n, n = 5,7,9 and C_n⁺, n = 4,5) and to simulate the mass spectrum of the acetylene molecule (C₂H₂).