Infrared spectroscopy and modeling of co-crystalline CO2·C2H2 aerosol particles. I. The formation and decomposition of co-crystalline CO2·C2H2 aerosol particles

Abstract

Aerosol particles composed of co-crystalline CO(2)·C(2)H(2) were generated in a bath gas cooling cell at cryogenic temperatures and investigated with infrared spectroscopy between 600 and 4000 cm(-1). Similar to results obtained for thin films of the co-crystal [T. E. Gough and T. E. Rowat, J. Chem. Phys. 109, 6809 (1998)], this phase was found to be metastable and decomposed into pure CO(2) and pure C(2)H(2). These decomposed aerosols were characterized through (i) a comparison to experimentally prepared aerosols of mixed CO(2) and C(2)H(2) of known architectures and (ii) the modeling of infrared spectra. A likely architecture after decomposition are C(2)H(2)-CO(2) core-shell particles with a disk-like shape. The co-crystalline CO(2)·C(2)H(2) aerosols prior to decomposition are modeled and analyzed in detail in the subsequent paper (Part II).

Infrared spectroscopy of solid mixed ammonia–water and acetylene–water aerosol particles

“…We find that ammonia-water and acetylene-water form amorphous molecularly mixed aerosol particles in a bath gas cooling cell at 78 K. This differs from results for acetylene-carbon dioxide [29,30], ammonia-acetylene [31], and water-carbon dioxide [32] particles formed under similar conditions. The IR spectra of these particles exhibit distinct features that allow their identification and clear distinction from pure particles and mixed hydrate particles.…”

“…There were no significant changes observed in any of the spectra over a measurement time of 30 minutes. The spectrum of pure acetylene particles (trace (a)) most resembles that of orthorhombic polycrystalline (partially amorphous) particles [29,31,48,62,63]. Thin films of acetylene were also found to be polycrystalline at 63 K [10].…”

“…We have previously studied other binary mixed aerosol particles containing water, ammonia, or acetylene that may be relevant for astrophysical studies, such as acetylenecarbon dioxide particles [29,30], ammonia-acetylene particles [31], and water-carbon dioxide particles [32]. While all these experiments were performed under similar conditions, each of the binary mixed aerosol systems was found to have different shapes, architectures, and internal structures.…”

“…These different particle properties can have a dramatic effect on the band shapes in the IR spectra. Acetylene and carbon dioxide were found to immediately form metastable co-crystalline aerosol particles that decomposed to pure acetylene and pure carbon dioxide with time [29,30]. In contrast, acetylene formed a co-crystal with ammonia via solid-state diffusion after the initial formation of core-shell particles [31].…”

Atmospheric processes on ice nanoparticles in molecular beams

“…The details of ice nanoparticles generation in supersonic expansions has been recently investigated by Kim et al (2004), Manka et al (2012), and Li et al (2013). The individual particles can be investigated under controlled conditions in vacuum by various means: e.g., ionization (electron, photon) and mass spectrometry (MacTaylor and Castleman, 2000; Lengyel et al, 2012b); infrared (IR) spectroscopy (Yacovitch et al, 2011; 2012; Preston et al, 2012; Fujii and Mizuse, 2013) or ultraviolet (UV) photodissociation experiments (Kreher et al 1999; Li and Huber, 2001; Poterya, et al 2007, 2008a; 2011; Ončák et al, 2008, 2011); particle (electron, photon, neutron) scattering (Heath et al, 2002; Kim et al, 2004; Manka et al, 2012); special methods such as sodium doping and subsequent spectroscopies (Bobbert et al, 2002; Yoder et al, 2011; Pradzynski et al, 2012). Such experiments provide unprecedented molecular-level insight into the small particle generation, their (photo)chemistry and (photo)physics and detailed dynamics of the processes on/in these particles.…”