TPD traces for key species obtained following exposure of toluene to a low H-atom fluence of 2.2 × 10¹⁸ cm⁻². (a) TPD trace for toluene (92 amu) in orange. (b) TPD traces, on a different Y axis scale, for partially hydrogenated toluene (parent mass 96 amu, main fragment 81 amu) in light blue and methyl-cyclohexane (parent mass 98 amu, main fragment 83 amu) in dark blue. The vertical grey lines show the desorption peaks of the three different molecules. Toluene desorbs at the highest temperature at 202 K, the partially hydrogenated toluene desorbs at 196 K, and the methyl-cyclohexane desorbs at the lowest temperature at 191 K.