(top-left) Average TPD curve for the ca. 955 cm⁻¹ feature. These data are fit to the functional form indicated in the inset. (middle-left) Derivative of this fit function compared to the m/z = 86–88 amu mass channels for experiment F. (top- and middle-right) Fragmentation patterns for diacetyl and acetoin, obtained from the NIST database. (bottom) Final adjusted difference spectrum shown in Figure 3 compared to the calculated infrared absorption spectrum of acetoin obtained at the CAM-B3LYP/def2-tZVP level of theory. Harmonic frequencies are scaled by a factor of 0.93.