15min:
EMPLOYING DIFFUSION MONTE CARLO IN THE CALCULATION OF MINIMIZED ENERGY PATHS OF THE CH3+ + H2 leftrightarrow CH5+ leftrightarrow CH3+ + H2 REACTION AND ITS ISOTOPIC VARIANTS.

CHARLOTTE E. HINKLE, ANNE B. MCCOY, Department of Chemistry, The Ohio State University, Columbus, OH 43210.

Protonated methane is presumed by astrochemists to be an important intermediate in the reaction CH3+ + HD rightarrow CDH4+ rightarrow CH2D+ + H2 within the interstellar medium. Understanding this reaction can also help shed light on the observed nonstatistical H/D isotopic abundance in the isotopologues of CH3+ within the interstellar medium. Interestingly, based on kinetic studies, Gerlich and co-workers showed that all of the reactions in the series CH3-nDn+ + HD rightarrow CH4-nDn+1+ rightarrow CH2-nDn+1+ + H2 have identical net rate constants . This result is independent of the value of n.

~

In previous studies of CH5+, we have employed Diffusion Monte Carlo (DMC) to study ground, and excited states.,, By performing the simulation in Jacobi coordinates, we can use Adiabatic DMC to study the properties of the minimized energy paths of CH5+ and isotopologues. To determine the minimized energy path, we calculate the quantum zero-point energy and ground state wave function as a function of the distance between the center of mass of the H2 group and the center of mass of the CH3+ group over a range from 0 to 6 \mathrmÅ. Over this range, we find 5 distinct regions of interaction, short range repulsion region, CH5+ complexation, short-range fragment interaction, long-range fragment interaction, and a region of no interaction between the two fragments. Interestingly, the range of H2/CH3+ distances spanned by each of the regions is roughly independent of the number or location of the deuterium atoms. Interestingly, the range of H2/CH3+ distances spanned by each of the regions is roughly independent of the number or location of the deuterium atoms.