Ab Initio Mass Spectrometry

Karl K. Irikura                                         Research Opportunity Number 50.64.61.B8431

Despite its major importance in chemical analysis, mass spectrometry still lacks theories that can provide computational predictions useful to the analyst. Mass spectrometry encompasses a variety of experimental techniques, requiring a variety of phenomena to be modeled. The cross-cutting phenomenon is unimolecular reaction kinetics; the branching among competing reactions is what determines relative peak intensities in a mass spectrum. A theoretical approach must include automatic discovery of reactions and their rates. Some tandem methods (CID, IRMPD) may be modeled as occurring on the ground electronic state. Electron ionization mass spectrometry (EIMS), arguably the most important technique in mass spectrometry, may require diabatic or non-adiabatic approaches. The energy deposition function must be modeled because it is critical to the relative dissociation rates. Finally, experimental spectra can only be simulated by modeling important instrumental biases, such as mass discrimination.