Supplementary material
The molecular structures of the two molecules studied in the present manuscript is presented
in Figure 1.
Figure 1. Molecular structures of Ibuprofen and Paracetamol molecules
Experimental section
Below a timing chart is depicted showing the procedure followed in the launch of the ion/laser
pulses and of the high voltage in the ion optics.
Figure 2. Timing chart of the experiment
Results and Discussion
As it is pointed out several times in the main manuscript all LPI spectra are
background corrected. The procedure followed is similar to that reported in [1] , meaning that
the signal corresponding to any residual photoionized gas phase species (below labeled as
"background signal") has been subtracted from the initial spectrum ((below labeled as
"background signal") , leaving only the contribution from sputtered neutrals that have been
post-ionized (below labeled as "background corrected signal"). Below are depicted the
aforementioned raw data for ibuprofen.
Figure 3. Raw LPI spectra of ibuprufen. The primary ion dose was 5x10 10 ions/cm2. Laser wavelength was 266
nm and the laser intensity at 5x1011 W/cm2.
The dependence of the detected photoion signal of several fragments on the laser
power was examined and presented below for the parent and the main molecular fragment
ions for paracetamol molecule.
Figure 4. Laser power dependence of the parent ion (m/z 151) and the characteristic molecular fragment of
paracetamol (m/z 109) under 266 nm, 150 ps laser post-ionization.
The single photon absorption as it is evident from the the fact that the slope in the in the loglog plot is less than unity (0.7±0.02) for both ions indicates that both the m/z 151 and m/z 109
ions are formed either through the dissociation of already ionized precursors or they are
formed from the corresponding sputtered neutral species which are subsequently ionized
through the first excited electronic state which lies close to the wavelength used in the present
study [2]. The same behaviour was also observed for the case of ibuprofen.
1. Willingham, D., Brenes, D. A., Wucher A., Winograd, N.: Strong-field Photoionization of Sputtered
Neutral Molecules for Molecular Depth Profiling. J. Phys. Chem. C, 114, 5391-5399 (2010).
2. www.nist.gov