SiO Molecules Research Articles

An interferometric search for SiO maser emission in planetary nebulae

Maser emission of SiO, H$_2$O, and OH is widespread in asymptotic giant branch (AGB) stars with oxygen- (O-) rich envelopes. This emission quickly disappears during the post-AGB phase and is extremely rare in planetary nebulae (PNe). So far, only eight PNe have been confirmed to show OH and/or H$_2$O maser emission, and none have ever been found to show SiO maser emission. We intend to obtain the first detection of a SiO maser from a PN. Such a detection would provide us with a useful tool to probe mass loss in PNe at a scales of a few AU from the central star, much shorter than the scales traced by H$_2$ or OH masers. We compiled two different samples. The first one comprises all known PNe with confirmed OH and/or H$_2$O maser emission, as well as two candidate PNe showing OH masers. For the second sample, we compiled single-dish SiO maser detections in the literature, and compared them with catalogs of PNe and radio continuum emission (which could trace photoionized gas in PNe). We identified five targets (either PN or radio continuum sources) within the beam of the single-dish SiO maser observations. We then carried out interferometric observations of both samples with the Australia Telescope Compact Array, to confirm the spatial association between continuum and SiO maser emission. We find no SiO maser emission associated with any confirmed or candidate PN. In all targets, except IRAS 17390$-$3014, there is no spatial coincidence between SiO masers and radio continuum emission. While in IRAS 17390$-$3014 we cannot completely rule out a possible association, it is unlikely that the radio continuum emission arises from a PN. The absence of SiO maser emission in PNe showing OH or H$_2$O masers is of special interest, since thermal SiO emission has been reported in at least one of these targets, indicating that SiO molecules can be present in the gas phase. Since some maser-emitting PNe show evidence of having O-rich outer envelopes, and carbon- (C-) rich central stars and inner envelopes, we speculate that SiO abundance could be very low in the central regions where physical conditions are optimal for maser pumping, and C-bearing molecules may be dominant in the gas phase at those locations.

Formation mechanism and luminescence properties of silicon carbide nanowires with core-shell structure

For the preparation of SiC nanowires (SiC NWs) by carbothermal reduction, it is of great significance to study the formation mechanism of sic nanowires for process optimization and the controllable preparation. Although first-principles molecular dynamics (FPMD) can simulate systems of hundreds of atoms on a picosecond time scale, the results of FPMD are still insufficient to elucidate the formation mechanism of core-shell SiC nanowires. To make up this deficiency, this article has conducted Deep Potential Molecular Dynamics (DPMD) simulation on nanoseconds timescales with near FPMD accuracy for systems containing thousands of atoms, the results more concretively show the formation process of core-shell SiC nanowires. DPMD simulation results show when CO molecules react with SiO molecules, CO molecules are wrapped by SiO molecules to form agglomerates, SiO molecules in the agglomerates that can come into contact with the wrapped CO molecules will react with wrapped CO molecules to form the SiC core, and SiO molecules that in the outer layer of the agglomerates will disproportionate into the amorphous SiO2 shell. Furthermore, the formation mechanism of SiC nanowires was validated in combination with thermodynamics and experimental methods. Thermodynamic results show that vacuum conditions are favorable for the formation of SiO and CO and lower the temperature of SiC preparation. Finally, the core-shell structure of SiC NWs with good luminescence properties were successfully prepared by carbothermal reduction method using carbon black and silicon dioxide as raw materials under the pressure of less than 5 kPa.

Dielectric behaviour, impedance and conductivity studies of YBaYbSiO oxy-apatite compounds

This paper reports the dielectric behaviour and electrical conduction properties of Y6-xBa4Ybx(SiO4)6O2 (YBaSiO: xYb) compounds. The Scanning Electron Microscopy (SEM) was utilized to obtain the surface microstructure of the compound. The micrographs showed both the circular and elongated shape of grains and their random distribution. The Fourier Transform Infrared Spectroscopy (FTIR) was used to confirm the presence of bond formations in the compounds. From the spectra, it was observed that the peaks at 690 cm−1 and a band from 850 cm−1 to 998 cm−1 are due to the stretching frequency of Y-O molecules and Si-O molecules, respectively. The peak centred at 1464 cm−1 is of vibration modes of Ba2+ions. These peaks confirmed the formation of oxy-apatite compounds. Both the dielectric permittivity and dielectric loss, decreases with increasing values of frequency due to reduction in the polarization effects on the higher side of frequency. This is because the dipole orientation lags with the rapidly reversing alternating current (ac) field. The value of dielectric loss was found to range between, 0 – 3.5 in frequency ∼ 100 Hz and 0 – 0.5 in frequency ∼ 100,000 Hz, up to temperature 500 °C. The impedance value decreases and hence a. c. conductivity increases, at higher frequencies. The increment in ac values followed the universal power law. The Nyquist plot showed that the area under the curves reduces and hence indicates negative temperature coefficient of resistance i.e., NTCR behaviour of compounds. The obtained results suggest the utilization of compound in electrical devices as power loss component, solid oxide fuel cells, and capacitors etc.

Effect of Ti-Si-Fe alloy on the nitriding behavior of Si powder

Adding Ti-Si-Fe alloy to Si powder reduced the complete nitriding temperature of Si from 1450 °C to 1300 °C, greatly reducing the nitriding temperature of Si powder and the formation temperature of Si3N4 whiskers. At low temperature, Fe in Ti-Si-Fe alloy damaged the SiO2 film on the surface of Si and produced SiO (g), which was conducive for the indirect and direct nitridation of Si. The density functional theory (DFT) calculation results showed that the energy levels of SiO (g) molecules adsorbed by Fe broadened and moved towards lower energy levels, resulting in a decrease in the bonding strength and an increase in reaction activity of SiO (g) molecules. It was beneficial for the indirect nitridation reaction of 3SiO (g)+2N2 (g)=Si3N4 (s)+3/2O2 (g), and promoted the formation of α-Si3N4 whisker. The liquid phase formed by increasing temperature and Ti-Si-Fe alloy addition promoted the direct nitridation of Si. The activation energy of TiSi2 and Ti-Si-Fe alloy nitridation was 78.42 (KJ/mol) and 14.97 (KJ/mol), respectively. The nitridation of Ti-Si-Fe alloy was easier, and the pores and cracks generated by Ti5Si3 and TiSi2 step-by-step nitridation at low temperature in Ti-Si-Fe alloy provided pore channels for N2 transport and sufficient nitrogen for Si nitridation.

The effect of winds on atmospheric layers of red supergiants II. Modelling VLTI/GRAVITY and MATISSE observations of AH Sco, KW Sgr, V602 Car, CK Car, and V460 Car

Context. Mass loss plays a crucial role in the lives of massive stars, especially as the star leaves the main sequence and evolves to the red supergiant (RSG) phase. Despite its importance, the physical processes that trigger mass-loss events in RSGs are still not well understood. Recently, we showed that adding a semi-empirical wind to atmosphere models can accurately reproduce observed extensions in the atmospheres of RSGs, where the mass-loss events are taking place, particularly in the CO and water lines. Aims. By adding a static wind to a MARCS atmospheric model, we computed synthetic observables that match new interferometric data of the RSGs AH Sco, KW Sgr, V602 Car, CK Car, and V460 Car obtained with the VLTI/MATISSE and VLTI/GRAVITY instruments between August 2022 and February 2023. We also used archival VLTI/AMBER data of KW Sgr and VLTI/GRAVITY data of AH Sco. The MATISSE wavelength range includes the SiO molecule at 4.0 μm with a spectral resolution of R ~ 500. Methods. The model intensities with respect to the line-of-sight angle (μ) as well as the spectra and visibilities were computed using the stellar radiative transfer code TURBOSPECTRUM. We found the best-fit model, mass-loss rate, and best-fit angular Rosseland diameter for the observations. We simultaneously matched our model to the data, covering a wavelength range of 1.8–5.0 μm, which corresponds to the K, L, and M bands. Results. Our models reproduce the spectro-interferometric data over this wide wavelength range, including extended atmospheric layers of CO, H2O, and SiO. We obtain a range of Rosseland angular diameters between 3.0 < θRoss < 5.5 mas and a range of mass-loss rates of −6.5 < log Ṁ/M⊙ yr−1 < −4 for our five targets. In our best-fit models, the partial pressure of SiO relative to the gas pressure, PSiO/Pg, and the SiO 4.0 μm line intensity increase between 2 and 3 stellar radii. The relative intensity depends on the luminosity used for our models, since the more luminous models have a higher mass-loss rate. Conclusions. This work further demonstrates that our MARCS+wind model can reproduce the observed physical extension of RSG atmospheres for several spectral diagnostics spanning a broad wavelength range. We reproduce both spectra and visibilities of newly obtained data as well as provide temperature and density stratifications that are consistent with the observations. With the MATISSE data, we newly include the extension of SiO layers as a precursor of silicate dust.

The ALMA-QUARKS Survey. I. Survey Description and Data Reduction

This paper presents an overview of the QUARKS survey, which stands for “Querying Underlying mechanisms of massive star formation with ALMA-Resolved gas Kinematics and Structures.” The QUARKS survey is observing 139 massive clumps covered by 156 pointings at Atacama Large Millimeter/submillimeter Array (ALMA) Band 6 (λ ∼ 1.3 mm). In conjunction with data obtained from the ALMA-ATOMS survey at Band 3 (λ ∼ 3 mm), QUARKS aims to carry out an unbiased statistical investigation of massive star formation process within protoclusters down to a scale of 1000 au. This overview paper describes the observations and data reduction of the QUARKS survey, and gives a first look at an exemplar source, the mini-starburst Sgr B2(M). The wide-bandwidth (7.5 GHz) and high-angular-resolution (∼0.″3) observations of the QUARKS survey allow for the resolution of much more compact cores than those could be done by the ATOMS survey, and to detect previously unrevealed fainter filamentary structures. The spectral windows cover transitions of species including CO, SO, N2D+, SiO, H30 α, H2CO, CH3CN, and many other complex organic molecules, tracing gas components with different temperatures and spatial extents. QUARKS aims to deepen our understanding of several scientific topics of massive star formation, such as the mass transport within protoclusters by (hub-)filamentary structures, the existence of massive starless cores, the physical and chemical properties of dense cores within protoclusters, and the feedback from already formed high-mass young protostars.

Theoretical and experimental study of the mechanism for preparation of SiC nanowires by carbothermal reduction

High-quality SiC nanowires (NWs) were prepared at 1550 °C by carbothermal reduction of silica with carbon black under normal atmospheric pressure without a metallic catalyst. Linear and chain-beaded SiC NWs were synthesized in graphite and BN crucibles, respectively. The mass of the SiC NWs obtained from the BN crucible was greater than that obtained from the graphite crucible under the same conditions. Thermodynamic analyses and first-principles molecular dynamics simulations were performed to investigate the formation mechanism of the SiC NWs. Thermodynamic analysis revealed that in the carbothermal reduction reaction zone, SiO2 and C reacted to produce SiC particles, SiO, and CO. Subsequently, SiO reacted with CO during condensation, leading to the growth of SiC NWs. The first-principles molecular dynamics simulations indicate that the BN substrate has a greater affinity for gas-phase molecules than the graphite substrate, thereby creating optimal reaction sites for the reaction of SiO and CO molecules. This study provides a valuable reference for understanding the microscopic formation mechanisms and the large-scale production of SiC NWs.

Imaging Photodissociation Dynamics of Excited SiO Molecules at 193 nm with Laser Ablation Supersonic Beam

Imaging Photodissociation Dynamics of Excited SiO Molecules at 193 nm with Laser Ablation Supersonic Beam

PHYSICAL PROPERTIES AND KINEMATICS OF DENSE CORES ASSOCIATED WITH REGIONS OF MASSIVE STAR FORMATION FROM THE SOUTHERN SKY

The results of spectral observations in the \( \sim {\kern 1pt} 84{\kern 1pt} - {\kern 1pt} 92\) GHz frequency range of six objects from the southern sky having dense cores and associated with massive star and star cluster forming regions are presented. The observations are carried out with the MOPRA-22m radio telescope. Within the framework of the local thermodynamic equilibrium (LTE) approximation, column densities and abundances of the H13CN, H13CO+, HN13C, HC3N, c-C3H2, SiO, CH3C2H and CH3CN molecules are calculated. Kinetic temperatures (\( \sim 30{\kern 1pt} - {\kern 1pt} 50\) K), sizes of emission regions (\( \sim 0.2{\kern 1pt} - {\kern 1pt} 3.1\) pc) and virial mass esimates (\( \sim 70{\kern 1pt} - {\kern 1pt} 4600{\kern 1pt} {{M}_{ \odot }}\)) are obtained. The linewidths in the three cores decrease with increasing distance from the center. Four cores exhibit asymmetry in the profiles of the optically thick HCO+(1–0) and HCN(1–0) lines, indicating the presence of systematic motions in the line of sight. In two cases, the asymmetry can be caused by contraction of gas. The model HCO+(1–0) and H13CO+(1–0) spectral maps obtained within the non-LTE spherically symmetric model are fitted into observed ones. Radial density (\( \propto {\kern 1pt} {{r}^{{ - 1.6}}}\)), turbulent velocity (\( \propto {\kern 1pt} {{r}^{{ - 0.2}}}\)) and contraction velocity (\( \propto {\kern 1pt} {{r}^{{0.5}}}\)) profiles in the G268.42–0.85 core are obtained. The contraction velocity radial profile differs from expected both in the case of free fall of gas onto a protostar (\({{r}^{{ - 0.5}}}\)), and in the case of global core collapse (contraction velocity does not depend on distance). A discussion of the results obtained is provided.

Dust Coagulation in Oxygen-rich Circumstellar Outflows

We show that the inefficient growth of SiO molecules on (SiO) x dust grains prolongs the period of maximum dust nucleation in circumstellar outflows resulting in a several orders-of-magnitude increase in the dust density near the star. This increase in dust density powers dust coagulation and results in the formation of large fractal aggregates that should be extremely efficient per unit mass in coupling to both the stellar radiation field and to the ambient gas.

The diffusion characteristics of POSS under electric field and non-uniform temperature field in natural ester insulating oil

The natural ester insulating oil is a green and environmentally friendly liquid dielectric, and nano additives can effectively improve its dielectric and heat transfer performance. However, nano additives are prone to agglomeration, especially under the influence of electric and temperature fields, which can impact the prolonged stable operation of power transformers. In this paper, the diffusion properties of caged Polysilsesquioxane (POSS) molecules in natural ester insulating oil under external electric field and non-uniform temperature field were investigated via simulation, and the effects of temperature and electric field on POSS molecules were expounded from the perspective of interaction. The results show that the high temperature difference and strong electric field can effectively improve the mobility of POSS molecules, and the temperature difference has a greater impact on the diffusion. The decrease of interaction energy is mainly due to the negative positive interaction between Si-O molecules in POSS molecules and insulating oil at high temperature, which counteracts the attraction of branch chains. At the same time, POSS molecules in the electric field will also show obvious polarization due to temperature changes, which further reduces the interaction between POSS molecules and insulating oil molecules. In addition, the electrostatic interaction energy decreases most obviously, which is the main reason that affects the migration characteristics of POSS molecules in natural ester insulating oil. This study provides a theoretical explanation for the migration mechanism of insulating oil in the microenvironment.

Time-Dependent Power-Law Growth of Oxide with Anomalous Diffusion in the Thermal Oxidation of 4H-SiC\((11\bar{2}0)\) and 4H-SiC\((000\bar{1})\)

A model for the oxide growth in the thermal oxidation of SiC with a non-polar surface orientation is proposed. It is based on the reaction–diffusion equations (RDEs), in which the diffusion of both SiO and O2 molecules is considered. By taking the 4H-SiC\((11\bar{2}0)\) a-face as an example, the RDEs are integrated numerically at the oxidation temperature of T = 1150 °C and the partial pressure of oxygen molecules in the ambient environment of Pox = 0.25, 0.5, 1, 2, and 4 (atm). By analyzing the simulation results on the evolution of the oxide thickness xo, it is found that xo obtained by the simulations and those of the experiments reported in the literature collapse onto a single curve when they are plotted against the rescaled time t′ = (ωp/ω1)t, where t denotes the oxidation time and ωp is defined as ωp = Θs(Pox)νinc. Here, Θs(Pox) and νinc denote the steady-state density of the oxygen molecules chemisorbed on the oxide surface and the prefactor for the incorporation rate of the oxygen molecules from the oxide surface into the oxide layer, respectively; ω1 is a constant, which is given by \(\omega_{1} = \omega_{p}|_{P_{\text{ox}} = 1(\text{atm})}\). The curve yielded by the collapse is found to follow the time-dependent power law (TDPL) as xo(t) ∝ (t/τ)ν(t), where the exponent ν(t) is given by \(\nu (t) = 0.565 + 0.2/(1 + \sqrt{2t/\tau } )\) with τ [= 1 (h)] a constant. This property is found to be valid also for the oxidation of a polar surface, 4H-SiC\((000\bar{1})\), by comparing the results of the calculations according to xo(t) ∝ (t/τ)ν(t) with the experiments reported in the literature. Therefore, the oxide growth in these systems follows the TDPL with the anomalous diffusion of νD = 0.565, which is larger than the normal diffusion of νD = 0.5 observed in the thermal oxidation of Si. In addition, the transition between the etching mode at low Pox and the oxidation mode at high Pox on the 4H-SiC\((11\bar{2}0)\) a-face is found to occur at \(P_{\text{c}} \simeq 0.73\) (atm) at T = 1150 °C.

Mechanisms of SiO oxidation: Implications for dust formation

Reactions of SiO molecules have been postulated to initiate efficient formation of silicate dust particles in outflows around dying (AGB) stars. Both OH radicals and H2O molecules can be present in these environments and their reactions with SiO and the smallest SiO cluster, Si2O2, affect the efficiency of eventual dust formation. Rate coefficients of gas-phase oxidation and clustering reactions of SiO, Si2O2 and Si2O3 have been calculated using master equation calculations based on density functional theory calculations. The calculations show that the reactions involving OH are fast. Reactions involving H2O are not efficient routes to oxidation but may under the right conditions lead to hydroxylated species. The reaction of Si2O2 with H2O, which has been suggested as efficient producing Si2O3, is therefore not as efficient as previously thought. If H2O molecules dissociate to form OH radicals, oxidation of SiO and dust formation could be accelerated. Kinetics simulations of oxygen-rich circumstellar environments using our proposed reaction scheme suggest that under typical conditions only small amounts of SiO2 and Si2O2 are formed and that most of the silicon remains as molecular SiO.

Preparation and properties of alumina-carbon castables using SiC nanofiber coated graphite flake

SiC nanofiber coated graphite flakes were fabricated at a relatively low temperature of 1623 K via an in-situ catalytic reaction approach employing Co(NO3)2·6H2O as a catalyst precursor. The effects of catalyst amount and firing temperature on phase composition, morphology and water wettability of the as-prepared SiC nanofiber coated graphite flakes were studied. The Co catalyst promoted the growth of SiC nanofibers, which according to the density functional theory calculations, can be attributed to the increased bond length and weakened bonding of CO(g) and SiO(g) molecules upon their adsorption onto the Co catalyst. The water contact angle of SiC nanofiber coated graphite was reduced to 25° from that 111° in the case of its uncoated counterpart. Furthermore, Al2O3-C castables using SiC nanofiber coated graphite flakes exhibited 73.1 % higher residual CMOR ratio after thermal shock test, 20.0 % lower in oxidation, and 43.5 % less in slag corrosion, than their counterparts using uncoated graphite flakes.

Isobaric molar heat capacity model for the improved Tietz potential

AbstractIn this study, the improved Tietz potential was used to describe the internal vibration of diatomic molecules. By employing the expression for upper bound vibrational quantum number and canonical partition function of the system, equation for the prediction of constant pressure (isobaric) molar heat capacity of diatomic molecules was derived. The analytical model was used to predict the isobaric molar heat capacity of the ground state CO, BBr, HBr, HI, P2, KBr, Br2, PBr, SiO, and Cl2 molecules. The upper bound vibrational quantum number obtained for the molecules are 85, 100, 21, 21, 115, 301, 89, 157, 110, and 67. The calculated average absolute deviations are 2.3462%, 1.1342%, 2.3350%, 1.9078%, 0.7268%, 2.4041%, 1.7849%, 1.8989%, 2.5209%, and 2.1523% from experimental data. The results obtained are in good agreement with available literature data on gaseous molecules.

Toward controllable Si-doping in oxide molecular beam epitaxy using a solid SiO source: Application to β -Ga2O3

The oxidation-related issues in controlling Si doping from the Si source material in oxide molecular beam epitaxy (MBE) are addressed by using its solid suboxide, SiO, as an alternative source material in a conventional effusion cell. Line-of-sight quadrupole mass spectrometry of the direct SiO-flux (ΦSiO) from the source at different temperatures (TSiO) confirmed SiO molecules to sublime with an activation energy of 3.3 eV. The TSiO-dependent ΦSiO was measured in vacuum before and after subjecting the source material to an O2-background of 10−5 mbar (typical oxide MBE regime). The absence of a significant ΦSiO difference indicates negligible source oxidation in molecular O2. Mounted in an oxygen plasma-assisted MBE, Si-doped β-Ga2O3 layers were grown using this source. The ΦSiO at the substrate was evaluated [from 2.9 × 109 cm−2 s−1 (TSiO = 700 °C) to 5.5 × 1013 cm−2 s−1 (TSiO = 1000 °C)] and Si-concentration in the β-Ga2O3 layers measured by secondary ion mass spectrometry highlighting unprecedented control of continuous Si-doping for oxide MBE, i.e., NSi from 4 × 1017 cm−3 (TSiO = 700 °C) up to 1.7 × 1020 cm−3 (TSiO = 900 °C). For a homoepitaxial β-Ga2O3 layer, a Hall charge carrier concentration of 3 × 1019 cm−3 in line with the provided ΦSiO (TSiO = 800 °C) is demonstrated. No SiO-incorporation difference was found between β-Ga2O3(010) layers homoepitaxially grown at 750 °C and β-Ga2O3(−201) heteroepitaxial layers grown at 550 °C on c-plane sapphire. However, the presence of activated oxygen (plasma) resulted in partial source oxidation and related decrease in doping concentration (particularly at TSiO < 800 °C), which has been tentatively explained with a simple model. Degassing the source at 1100 °C reverted this oxidation. Concepts to reduce source oxidation during MBE-growth are referenced.

Polarization Transfer Rates by Isotropic Collisions between Astrophysical SiO Molecule and Electrons

We are interested in quantum calculations of polarization transfer (PT) rates due to collisions of the SiO molecule with the electrons. We determine the inelastic PT rates associated to the transitions: X 1Σ+→3Π; X 1Σ+→3Σ+; X 1Σ+→3Δ; X 1Σ+→3Σ−. In addition, we calculate the elastic PT rates due to rotational transitions inside the electronic state X 1Σ+ which are related to observed astronomical SiO MASERs. Our PT rates are obtained through linear combination of excitation rates previously calculated for SiO-electron collisions. The calculations are performed on a collision energy grid large enough to ensure converged state-to-state rates for temperatures ranging from 1000 to 10,000 K for inelastic rates and from 5 to 5000 K for elastic rates. The dependence of the inelastic rates on temperatures is obtained analytically and given in useful form.

СОНОЛЮМИНЕСЦЕНТНАЯ СПЕКТРОСКОПИЯ КОЛЛОИДНЫХ СУСПЕНЗИЙ: МОЛЕКУЛЯРНАЯ, ИОННАЯ И АТОМАРНАЯ ЛЮМИНЕСЦЕНЦИЯ ПРИ СОНОХИМИЧЕСКОМ РАЗЛОЖЕНИИ НАНОЧАСТИЦ ДИОКСИДА КРЕМНИЯ, СОДЕРЖАЩИХ СОЕДИНЕНИЯ РУТЕНИЯ И МЕДИ

The article is devoted to an example of the sonoluminescence spectroscopy use, which was previously known as a method for analyzing substances from the characteristic spectra of their sonoluminescence only in true solutions, for carrying out a similar analysis of substances contained in insoluble nanoparticles in colloidal suspensions. The solutions sonolysis, that is, their irradiation with ultrasound, is accompanied by the formation of cavitation bubbles that vibrate radially at the frequency of the ultrasonic field. Volatile components of the solution enter the bubbles, evaporating from the liquid-gas interface; nonvolatile components can penetrate into the bubble as a result of the injection of solution nanodroplets into the gas phase, which occurs during intense bubble movements accompanied by their deformation. In a nonequilibrium plasma periodically forming in cavitation bubbles, destruction occurs, as well as collisional excitation of these components, followed by luminescence. It has been shown that this mechanism of sonoluminescence also operates in colloidal suspensions, where substances are present in the form of nanoparticles with sizes less than 50 nm. Such nanoparticles penetrate into moving cavitation bubbles, without destroying them, as part of nanodroplets, and then undergo decomposition in bubble plasma with the excited particles generation as emitters of characteristic sonoluminescence. In this work, we synthesized colloidal suspensions in dodecane of porous SiO2 nanoparticles containing adsorbed Ru(bpy)3Cl2 and CuSO4 salts. During moving single-bubble sonolysis for these suspensions, characteristic emission spectra of Ru and Cu atoms, SiO molecules, and Ru(bpy)3 ions suitable for sonoluminescence spectroscopic analysis were recorded. By comparing the experimental and calculated (at different temperatures) luminescence spectra of Ru atoms, we estimated the electron temperature attained upon acoustic compression of single bubble in colloidal suspension in dodecane: Te = 7000 K.

Silicon determination via a SiO rotational line using high-resolution graphite furnace molecular absorption spectrometry: A straightforward approach for the analysis of solid samples prepared as suspensions

High-resolution graphite furnace molecular absorption spectrometry combined with samples prepared as suspensions were used for the quantification of Si in geological samples and in spent catalysts used for petrochemical processing. Measurements at the main Si resonance line at 251.6110 nm were proven unfeasible due to the formation of a quasi-continuous signal, which resulted in significant memory effect. An alternative was to monitor the fine rotational spectrum of SiO, which allowed memory effect-free measurements. A SiO rotational line centered at 231.9373 nm was selected to carry out quantitative analysis of Si at high percent concentrations in a variety of solid samples. Pyrolysis and vaporization temperatures were evaluated and optimized as 800 °C and 2400 °C, respectively, without the need to use a chemical modifier. Attempts to produce SiO molecules from acidified aqueous standards containing Si were unsuccessful, as the molecule could only be produced from solid samples, likely due to the formation mechanism that involves thermal decomposition of silicates. Hence, solid samples were prepared as suspensions in 0.14 mol L−1 HNO3. Calibration was performed using a series of suspensions prepared from a gabbro rock certified reference material (CRM), resulting in a limit of detection of 0.5% (m/m). The accuracy of the method was attested by the analysis of several CRM, including rocks, soils and sediments. Solid spent petrochemical catalyst samples were also analyzed and 97–114% recovery was obtained by spiking the catalyst suspensions with a CRM. The good accuracy demonstrated that the formation of SiO is free from matrix effects and highly efficient under the adopted conditions. Overall, the method was proven accurate and consists on a simple and fast alternative to determine Si in silicate-rich samples.

Searching for shocks in high-mass starless clump candidates

ABSTRACT In order to search for shocks in the very early stage of star formation, we performed single-point surveys of SiO J = 1–0, 2–1, and 3–2 lines and the H2CO 212−111 line towards a sample of 100 high-mass starless clump candidates (SCCs) by using the Korean VLBI Network (KVN) 21-m radio telescopes. The detection rates of the SiO J = 1–0, 2–1, 3–2 lines, and the H2CO line are $31.0$, $31.0$, $19.5,$ and $93.0{{\ \rm per\ cent}}$, respectively. Shocks seem to be common in this stage of massive star formation. The widths of the observed SiO lines [full width at zero power (FWZP)] range from 3.4 to 55.1 km s−1. A significant fraction ($\sim 29{{\ \rm per\ cent}}$) of the detected SiO spectra have broad line widths (FWZP > 20 km s−1), which are very likely associated with fast shocks driven by protostellar outflows. This result suggests that about one third of the SiO-detected SCCs are not really starless but protostellar. On the other hand, about 40 ${{\ \rm per\ cent}}$ of the detected SiO spectra show narrow line widths (FWZP < 10 km s−1) probably associated with low-velocity shocks which are not necessarily protostellar in origin. The estimated SiO column densities are mostly 0.31−4.32 × 1012 cm−2. Comparing the SiO column densities derived from SiO J = 1–0 and 2–1 lines, we suggest that the SiO molecules in the SCCs may be in the non-LTE condition. The SiO abundances to H2 are usually 0.20−10.92 × 10−10.