Given an unidentified analyte, determining its molecular mass is a critical step towards confidently proposing its molecular structure. Electron ionization mass spectrometry (EI-MS) is one of the most widely employed techniques to elucidate chemical structure. In EI-MS, an analyte is ionized by impact with energetic electrons and the relative intensities of its resulting ions are recorded across a mass-charge range in a mass spectrum. A molecular ion is an ion of the intact molecule and the ions that result from fragmentation are fragment ions. If the resulting mass spectrum contains a molecular ion peak, the molecular mass of the analyte can be directly determined.