Structures and photoelectron spectroscopies of Si2C2- studied with ab initio multicanonical Monte Carlo simulation

Experimental photoelectron spectrum of Si2C2- was assigned by ab initio Mon te Carlo simulation with the multicanonical/histogram reweighting technique . At first, two structures, linear and ring, were optimized at the MP2/6-31 G* level. The multireference configuration interaction (MRCI) calculation r eveals that the spectrum cannot be assigned by considering only a single is omer. Also, MRCI calculations cannot explain different widths of the peaks in the spectrum. Multicanonical Monte Carlo simulation with configuration i nteraction calculation at each step of the simulation was performed for bot h ring and linear isomers to include the effects of large nuclear motion at finite temperature on the spectrum. It was found that a mixture of two iso mers at the experimental condition is necessary to assign the spectrum.