The ion–molecule reaction after multiphoton ionization in the binary cluster of ammonia and methanol

The binary cluster (CH3OH)n(NH3)m was studied by using a multiphoton ionization time-of-flight mass spectrometer (MPI-TOFMS). The measured two series of protonated cluster ions: (CH3OH)nH+ and (CH3OH)nNH4+ (1≤n≤14) were attributed to the ion–molecule reaction in the binary cluster ions. The mixed cluster of CH3OD with ammonia was also studied. The results implied that the proton transfer probability from the OD group was larger than that from CH3 group. The ab initio calculation of the binary cluster was carried out at the HF/STO-3G and MP2/6-31G∗∗ levels of theory, and indicated that the latter process of the proton transfer must overcome a barrier of ∼29 kcal/mol.