Conformity of the 7-azaindole dimer cationic potential with photoionization/Coulomb-explosion MS observations and the concerted biprotonic transfer mechanism

In this Letter we consider the second laser-pulse time delay experiments of Castleman and co-workers [D.E. Folmer, L. Poth, E.S. Wisniewski, A.W. Castleman, Jr., Chem. Phys. Lett. 287 (1998) 1; D.E. Folmer, E.S. Wisniewski, S.M. Hurley, A.W. Castleman, Jr., Proc. Natl. Acad. Sci. USA 96 (1999) 12980] as interrogating the (density functional theory) biprotonic phototautomerization as correlated with the cationic doublet ground electronic state potential D0(+) for the species produced in the photoionization step. We demonstrate that the 7-AI(H+) cation can result as a product of this photoionization, and is then revealed a Coulomb-explosion time-of-flight mass spectrum (TOF–MS) species. We demonstrate that the mass-119/mass-118 ratios as a function of photoionization, and Coulomb-explosion laser pulse delay can conform to the concerted biprotonic mechanism. The interpretation emphasizes the invasive nature of the TOF–MS technique requirement in studying the excited state of the doubly-H-bonded 7-azaindole dimer.