The Ratio of Metastable Fragmentation of the E1wnh+ Cluster at VE/VS=5% Is Shown in Fig

Electronic supplementary material to the manuscript: Insights onclusters formation mechanism by Time Of Flight Mass Spectrometry. 1. The Case of Ethanol–Water Clusters.

X. Li 1, 2, X. Wang 3, M. Passaro 4, N. Spinelli 5, B. Apicella 1[1]

1Istituto di Ricerche sulla Combustione, IRC–CNR, P.le Tecchio 80, 80125 Napoli, Italy

2Key Laboratory of Power Machinery and Engineering, Ministry of Education, ShanghaiJiaoTongUniversity, Shanghai 200240, China

3SPIN - CNR, Via Cintia, 80124 Napoli – ITALY

4Istituto di Ricerche sulla Combustione, IRC–CNR and Chemical Engineering, Materials and Industrial Production Department, University of Naples “Federico II,” P.le Tecchio 80, 80125 Napoli, Italy

5CNISM and Physics Department, University of Naples “Federico II,” Via Cintia, 80124 Napoli, Italy

Mass spectra of pure water clusters by TOFMS with EI and PI are reported in Figs. ESM. 1a and b, respectively. The mass of the higher peaks are indicated (m/z= 73 and 91).

ESM. 1 Mass spectra of pure water clusters acquired with EI ionization (a) and laser PI (b).

Clusters mass spectra obtained both with EI and PI for ethanol (E) -water (W) mixtures at VE/VS =20% are presented inFigs. ESM. 2 a and b.The clusters family at fixed E and variable W are grouped in the figures, showing the main peak of each family attributable to neat ethanol clusters, starting from the dimer.

ESM. 2Mass spectra of clusters at 20%VE/VSethanol/solution ratio with EI (a) and with laser PI (b).

ESM.3 Intensity distributions of EmWp-nH+(p= 19-24, m=3-5). The error bars of the intensities are smaller thanthe diameters ofthe circles.

ESM.4Composition distribution of ethanol-water clusters, in terms of the number of water molecules (n) and ethanol molecules (m) determined in each cluster, at 20% VE/VSethanol/solution ratio with EI (a) and with laser PI (b).

ESM.5Autocorrelation of water clusters spectra at 20% VE/VS ethanol/solution ratio with EI(a) and with laser PI (b). Labels for mixed ethanol-water, pure water (black, bolded) and pure ethanol (magenta, bolded) clusters are reported too.

The parameter I200~1000/I50~200at VE/VS=5% and 40% with different laser poweris shownin Figs. ESM. 6a and bwhere I200~1000 is the sum of the intensities of peaks in the MW range 200-1000 Da whereas I50~200 is the sum of the intensities of peaks in the MW range 50-200 Da, as introduced in the paper.

I200~1000/I50~200 ratio significantly decreases with increasing the PD, which suggests that the smaller molecular masses dominate the spectra with increasing laser power. This is due to a larger fragmentation occurring in the ionization region with increasing laser power. It can be obviously observed that the lower I200~1000/I50~200 ratio value and, therefore, the higher fragmentation can be produced by using EI, even in comparison with the maximum PD as shown in Figs.ESM.2a and b.

ESM. 6 Variation of I200-1000/I50-200 for clusters of ethanol–water binary mixture solution at (a) VE/VS=5% and (b) VE/VS=40% with increasing the PD.

[1]Author to whom correspondence should be addressed: Dr. Barbara Apicella.Electronic mail: