Ionization of Ammonia Nanoices with Adsorbed Methanol Molecules

Abstract

Large ammonia clusters represent a model system of ices which are omnipresent throughout the space. The interaction of ammonia ices with other hydrogen-boding molecules such as methanol or water and their behavior upon an ionization are thus relevant in the astrochemical context. In this study, ammonia clusters (NH3)N with the mean size N¯ ≈230 were prepared in molecular beams and passed through a pickup cell in which methanol molecules were adsorbed. At the highest exploited pickup pressures, the average composition of (NH3)N(CH3OH)M clusters was estimated to be N:M≈ 210:10. On the other hand, the electron ionization of these clusters yielded about 75% of methanol-containing fragments (NH3)n(CH3OH)mH + compared to 25% contribution of pure ammonia (NH3)nH + ions. Based on this substantial disproportion, we propose the following ionization mechanism: The prevailing ammonia is ionized in most cases, resulting in NH + 4 core solvated most likely with four ammonia molecules, yielding the well-known "magic number" structure (NH 3 ) 4 NH + 4 .The methanol molecules exhibit strong propensity for sticking to the fragment ion. We have also considered mechanisms of intracluster reactions. In most cases, proton transfer between ammonia units take place. The theoretical calculations suggested the proton transfer either from the methyl group or from the hydroxyl group of the ionized methanol molecule to ammonia to be the energetically open channels. However, the experiments with selectively deuterated methanols did not show any evidence for the D + transfer from the CD 3 group. The proton transfer from the hydroxyl group could not be excluded entirely nor confirmed unambiguously by the experiment.

Few-cycle laser driven reaction nanoscopy on aerosolized silica nanoparticles

“…The concentration and enhancement of electromagnetic fields on the nanoscale is important for many applications including detection of trace substances 7 , single-molecule spectroscopy and microscopy 8,9 , as well as nanofocusing and modification of surfaces beyond the optical diffraction limit 10,11 . Isolated nanograins, nanoice, and other nanoparticles are known to play an important role in astrochemistry 12 , enabling the (irradiation-induced) formation of complex molecules and molecular ions 13 . How these formation processes are influenced by the morphology of the nanosurfaces is, however, largely unknown and strongly motivates experimental progress in this area.…”

Stabilization of benzene radical anion in ammonia clusters

“…It can be compared to the binding energy of an NH 3 molecule in clusters. For neutral ammonia dimer it is about 0.14 eV, 32,33 and it increases to 0.33 eV in the bulk. 32 The binding energies for our finite size negatively charged clusters are probably in the same energy region.…”

Understanding the Formation and Growth of New Atmospheric Particles at the Molecular Level through Laboratory Molecular Beam Experiments

“…The clusters generated by supersonic expansion pass through a skimmer into a differential pumping chamber where organics (e. g., methane, [117] olefins, [118] alkynes, alcohols, [119][120] organic acids [121][122] ) and N x O y and hydrogen halides [97,117] can be added. In recent years, more and more experimental attention has been paid to the study of sodium doped clusters, including NaPI (Sodium doping and photoionization, see more details in 2.3 below).…”

“…The analyzed sample should first be ionized, and then the ions should be separated according to the mass-to-charge ratio (m/z) to obtain the mass spectrometry by using the different behavior of different ions in the electric field or magnetic field, and the qualitative and quantitative results of the sample can be obtained through the mass spectrum and related information of the sample. Common mass spectrometry methods in the laboratory, such as time-of-flight (TOF) mass spectrometer, [17,99,[119][120]141] quadrupole mass spectrometer (QMS) [64,94,129] and fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer [142] etc. Infrared measurement is also powerful in the analysis of structural features of carbon dioxide and propane clusters, [98,143] and in the study of the proton vibrations of hydrated hydrogen halide clusters.…”