Schematic picture of the experimental apparatus CLUB: clusters are formed in MB Source chamber, the beam passes through several vacuum chambers, pumped differentially by diffusion (DP) and turbomolecular (TMP) pumps (pumping speeds specified); after ≈1.3 m the beam is analysed using reflectron time-of-flight mass spectrometer (RTOF MS). Velocity map imaging (VMI) and quadrupole mass spectrometry (QMS) are not exploited in the present study.
Detail of the mass spectra in 163–173 Da region: (a) 8% and (b) 0.7% acetylene in argon expansions. The black filled peaks in (a) represent the background signal for comparison. The strong dehydrogenation of (C2H2) n CH+ ions in pure acetylene clusters (a) is indicated in contrast to the mixed clusters (b).
Electron ionization mass spectra (10–180 Da range) of clusters formed in expansion of (a) 8% and (b) 0.7% acetylene in argon. The stagnation pressure was 3 bars and nozzle was kept at 223 K. Acetone impurities are labelled by stars.
Electron ionization mass spectra (180-2800 Da range) of clusters formed in the expansion of (a) 8% and (b) 0.7% acetylene in argon. The lower mass range of the same spectra is shown in Fig. 3 .
Near threshold part of energy dependent ion yields for selected cluster ions. Upper pannel (m/z = 78, triangles), (C2H2)2CH+ (m/z = 65, circles) and (C2H2)CH+ (m/z = 39, squares) ions detected in 8% acetylene expansion in argon. Lower panel Ar2(C2H2)+ (m/z = 106, squares) and (m/z = 132, circles)ions detected in 0.7% acetylene expansion in argon. Line represents appropriate fit used for appearance energy evaluation, evaluated appearance energies are marked by arrows.
Schematic representation of the electron ionization processes in acetylene and mixed Ar-acetylene clusters. [M n − k × H]+ labels formally evaporation of k H-atoms from M n cluster: these ions presumably correspond to some covalently bound molecular structures.
Appearance energies of the studied cluster ions related to the gas phase energies of involved species. The appearance energies from the present experiment can be found in the supplementary material; 26 the gas phase values were taken from literature referred in the text.
Selected ion decomposition reactions resulting in formation. Values in brackets are formation enthalpies in kcal/mole. These values and formation enthalpies Δ H r were taken from Refs. 2,4,24,33 .
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