Language：English  

DOI： 10.1021/acs.jpca.9b05434

Web of Science

PubMed

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/acs.est.9b00364

PubMed

Language：English  

DOI： 10.1063/1.5055684

PubMed

Other Link： http://orcid.org/0000-0002-5915-3576

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

Atmospheric particles contain a wide range of oligomers, but the formation mechanism and the origin of complexity are still unclear. Here, we report the direct detection of carbocationic oligomers generated from the exposure of a series of cyclic unsaturated hydrocarbon gases to acidic water microjets through interface-sensitive mass spectrometry. By changing gas concentrations, H2O (D2O) solvent, bulk pH and comparing results from experiments on acyclic, cyclic, and aromatic compounds, we elucidated three competing reaction mechanisms: chain propagation (CP), chain transfer (CT), and hydride abstraction (HA). We found that conjugative -electron delocalization in the carbocation is the most important factor for the interfacial oligomerization processes. Our results showed that electrophilic attack on C?C double bonds (CP and CT) is limited, and that on C-H single bonds (HA) is enhanced for carbocations lacking conjugation, which is not the case in bulk organic solutions. Carbocationic oligomers generated by the encounter of gaseous unsaturated hydrocarbons and acidic water surfaces potentially contribute to the molecular complexity in atmospheric particles.

DOI： 10.1039/c8cp04993a

Web of Science

PubMed

Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society ({ACS})  

DOI： 10.1021/acs.jpcc.8b08355

Language：English   Publisher：American Chemical Society ({ACS})  

DOI： 10.1021/acs.jpca.8b06914

PubMed

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Nature America, Inc  

Alumina (Al2O3) is believed to be the first major condensate to form in the gas outflow from oxygen-rich evolved stars because of the refractoriness and that α-Al2O3 (corundum, most stable polymorph) is a potential origin of a 13 μm feature that appears close to stars. However, no one has directly reproduced the 13 μm feature experimentally, and it has remained as a noteworthy unidentified infrared band. Here, we report nucleation experiments on Al2O3 nanoparticles monitored by a specially designed infrared spectrometer in the microgravity environment of a sounding rocket. The conditions approximate to those around asymptotic giant branch (AGB) stars. The measured spectra of the nucleated Al2O3 show a sharp feature at a wavelength of 13.55 μm and comparable in width to that observed near oxygen-rich AGB stars. Our finding that α-Al2O3 nucleates under certain condition provides a solid basis to elaborate condensation models of dust around oxygen-rich evolved stars.

DOI： 10.1038/s41467-018-06359-y

PubMed

Language：English   Publisher：American Chemical Society ({ACS})  

DOI： 10.1021/acs.jpca.8b04995

PubMed

Other Link： http://orcid.org/0000-0002-5915-3576

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

Recent studies have shown that atmospheric particles are sufficiently acidic to enhance the uptake of unsaturated volatile organic compounds (VOCs) by triggering acid-catalyzed oligomerization. Controlling factors of oligomerization at the aqueous surfaces, however, remain to be elucidated. Herein, isoprene (2-methyl-1,3-butadiene, ISO), 1,3-butadiene (1,3-b), 1,4-pentadiene (1,4-p), 1-pentene (1-p), and 2-pentene (2-p) vapors are exposed to an acidic water microjet (1 <= pH <= 5), where cationic products are generated on its surface within similar to 10 mu s and directly detected using surface-sensitive mass spectrometry. We found that carbocations form at the air-water interface in all the cases, whereas the extent of oligomerization largely depends on the structure in the following order: ISO >> 1,3-b 4 1,4-p >> 1-p approximate to 2-p. Importantly, the cationic oligomerization of ISO yields a protonated decamer ((ISO)(10)H+, a C-50 species of m/z 681.6), while the pentenes 1-p/2-p remain as protonated monomers. We suggest that ISO oligomerization is uniquely facilitated by (1) the resonance stabilization of (ISO) H+ through the formation of a tertiary carbocation with a conjugated CQC bond pair, and (2) pi-electron enrichment induced by the neighboring methyl group. Experiments in D2O and D2O: H2O mixtures revealed that ISO oligomerization on the acidic water surface proceeds via two competitive mechanisms: chain-propagation and proton-exchange reactions. Furthermore, we found that ISO carbocations undergo addition to relatively inert 1-p, generating hitherto uncharacterized co-oligomers.

DOI： 10.1039/c8cp01551a

Web of Science

PubMed

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.15011/jasma.35.3.350305

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

Crystalline ice formation requires water molecules to be sufficiently mobile to find and settle on the thermodynamically most stable site. Upon cooling, however, diffusion and rearrangement become increasingly kinetically difficult. Water ice grown by the condensation of water vapor in laboratory is thus generally assumed to be in a metastable amorphous form below 100 K. Here, we demonstrate the possibility of crystalline ice formation at extremely low temperature using a water/neon matrix (1/1000, 30000 monolayers) prepared at 6 K, which is subsequently warmed to 11-12 K. In situ infrared spectroscopy revealed the assembly of the dispersed water molecules, forming crystalline ice I during the sublimation of the neon matrix for 40-250 seconds. This finding indicates that the high mobility of the water molecules during matrix sublimation can overcome the kinetic barrier to form crystals even at extremely low temperature.

DOI： 10.1039/c7cp03315j

Web of Science

PubMed

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

Nucleation and subsequent rapid growth are enigmatic due to the unrevealed pathways. Despite the relatively simpler mechanism compared to nucleation and growth in solution, that in vapor has received little attention. The largest hindrance to unveiling this process may be observing the rapid and mesoscopic-scale phenomena. To overcome this hindrance, we combine an experimental approach with in situ spatial scanning Fourier-transform infrared spectroscopy, which reveals the nucleating and growing nanoparticles in vapor. The nanoparticles are then collected at different evolutionary stages and analyzed by ex situ transmission electron microscopy (TEM). Needle-shaped molybdenum oxide (MoO3) nanoparticles were formed within similar to 0.1 s after homogeneous nucleation from a highly supersaturated vapor. Over one second, the needle particles gradually evolved into a cubic shape by fusion in a crystallographically favored orientation in a free-flying state in vapor. The similar sizes of the elongated axes of the needle and cubic structures suggest an additional growth stage, in which the needle particles become the growth units of the cubic particles. The morphology of a final crystal should reflect the formation environment of the particle because growing crystals are sensitive to the formation conditions such as temperature, concentration, and impurities. Although nucleation under very high supersaturation induces the anisotropic growth of the needle particles, this information of the initial nucleation environment is lost in the final cubic crystal. These findings enrich our understanding of pathways in the nucleation and growth of nanoparticles and provide new insights into the growth stages driven by oriented attachment.

DOI： 10.1039/c7nr02613g

Web of Science

PubMed

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Multiple pathways in crystal nucleation are now known to be more common than previously predicted; it is, therefore, crucial to understand the early stages of crystallization. Even in relatively simple vapor-phase homogeneous nucleation, the process has significant potential diversity. Here, we experimentally show crystalline Al2O3 nanoparticles forming via precisely two steps in the nucleation process from supersaturated vapor with a moderate cooling rate. In situ FT-IR measurement of nucleation allowed us to observe the formation of Al2O3 nanoparticles. Liquid-like particles first nucleated from the vapor before crystallizing. The crystalline phase was preserved by quenching without further transformation into the most stable alpha-Al2O3 polymorph. The precipitated phase changed from delta-Al2O3 for pure Al2O3 to gamma-Al2O3 or theta-Al2O3 by adding Sb or Cr, respectively. We demonstrate that a two-step process occurs in homogeneous nucleation of refractory materials from supersaturated vapor, which may facilitate polymorphic control in industry formation in space. and improve understanding of cosmic dust

DOI： 10.1021/acs.chemmater.6b04061

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The formation of nanoparticles of titanium oxides by homogeneous nucleation from highly supersaturated vapors was investigated by in situ Fourier transform IR spectroscopy and by observation of the resulting nanoparticles by transmission electron microscopy (TEM). Titanium metal was thermally evaporated in a specially designed chamber under a gaseous atmosphere of oxygen and argon. Nano particles nucleated and subsequently grew as they flew freely through the oxidizing gas atmosphere. Nascent nanoparticles of titanium oxides showed a broad IR absorption band at 10-20 mu m. Subsequently, the cooled nanoparticles showed a sharp crystalline anatase feature at 12.8 mu m. TEM observations showed the formation of spherical anatase nanoparticles. The IR spectral evolution showed that the titanium oxides nucleated as metastable liquid droplets, and that crystallization proceeded through secondary nucleation from the supercooled liquid droplets. This suggests that history of the titanium oxide nanoparticles, such as the temperature and oxidation that they experience after nucleation, determines their polymorphic form. (C) 2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jcrysgro.2016.06.036

Web of Science

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1088/0004-637X

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We developed a new experimental system for infrared (IR) measurements on free-flying nucleating nanoparticles in situ and applied it to studies on silicate particles. We monitored the condensation of magnesium-bearing silicate nanoparticles from thermally evaporated magnesium and silicon monoxide vapor under an atmosphere of oxygen and argon. The IR spectrum of newly condensed particles showed a spectral feature for non-crystalline magnesium-bearing silicate that is remarkably consistent with the IR spectrum of astronomically observed non-crystalline silicate around oxygen-rich evolved stars. The silicate crystallized at &lt;500 K and eventually developed a high crystallinity. Because of the size effects of nanoparticles, the silicate would be expected to be like a liquid at least during the initial stages of nucleation and growth. Our experimental results therefore suggest decreasing the possible formation temperature of crystalline silicates in dust formation environments with relatively higher pressure.

DOI： 10.1088/0004-637X/803/2/88

Web of Science

Language：Japanese   Publisher：Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency(JAXA)(ISAS)  

Space Utilization Research (January 24-25, 2015. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency(JAXA)(ISAS)), Sagamihara, Kanagawa Japan

J-GLOBAL

Language：Japanese   Publisher：Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency(JAXA)(ISAS)  

Balloon Symposium 2015 (November 5-6, 2015. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (JAXA)(ISAS)), Sagamihara, Kanagawa Japan