Observation of the Water-HNSO2 Complex.

Sulfamic acid (NH2SO3H, SFA) is supposed to play an important role in aerosol new particle formation (NPF) in the atmosphere, and its formation mainly arises from the SO3-NH3 reaction system in which weakly bonded donor-acceptor complexes such as SO3···NH3 and isomeric HNSO2···H2O have been proposed as the key intermediates. In this study, we reveal the first spectroscopic observation of HNSO2···H2O in two forms in a solid Ar matrix at 10 K. The major form consists of two intermolecular H bonds by forming a six-membered ring structure with a calculated dissociation energy of 7.6 kcal mol-1 at the CCSD(T)-F12a/aug-cc-pVTZ level of theory. The less stable form resembles SO3···H2O in containing a pure chalcogen bond (S···O) with a dissociation energy of 7.2 kcal mol-1. The characterization of HNSO2···H2O with matrix-isolation IR spectroscopy is supported by D- and 18O-isotope labeling and quantum chemical calculations.

Spectroscopic identification of the ammonia-mercapto radical complex.

The elusive hydrogen-bonded radical complex (˙SH⋯NH3) consisting of ammonia (NH3) and a mercapto radical (˙SH) has been generated through the 193 nm laser photolysis of the molecular complex between NH3 and hydrogen sulfide (H2S) in solid Ar- and N2-matrixes at 10 K. The identification of ˙SH⋯NH3 with matrix-isolation IR spectroscopy and UV-vis spectroscopy is supported by 15N- and D-isotope labeling experiments and quantum chemical calculations at the B3LYP-D3(BJ)/6-311++G(3df,3pd) level of theory. In line with a large red shift of -172.2 cm-1 for the frequency of the S-H stretching mode observed in ˙SH⋯NH3 (cf. free ˙SH), the radical ˙SH acts as a hydrogen donor, and NH3 acts as an acceptor. According to the calculations at the CCSD(T)/aug-cc-pVTZ level, the SH⋯N bonded structure ˙SH⋯NH3 (binding energy De = 3.9 kcal mol-1) is more stable than the isomeric amidogen radical complex HSH⋯˙NH2 (De = 2.8 kcal mol-1) by 16.6 kcal mol-1. This is in sharp contrast to the photochemistry of the closely related HOH⋯NH3 complex, since the water-amidogen radical complex HOH⋯˙NH2 (De = 5.1 kcal mol-1) was generated under similar photolysis conditions, whereas the ammonia-hydroxyl radical complex ˙OH⋯NH3 (De = 7.9 kcal mol-1) is higher in energy by 9.3 kcal mol-1.

Unraveling sulfur chemistry in interstellar carbon oxide ices.

Formyl radical (HCO•) and hydroxycarbonyl radical (HOCO•) are versatile building blocks in the formation of biorelevant complex organic molecules (COMs) in interstellar medium. Understanding the chemical pathways for the formation of HCO• and HOCO• starting with primordial substances (e.g., CO and CO2) is of vital importance in building the complex network of prebiotic chemistry. Here, we report the efficient formation of HCO• and HOCO• in the photochemistry of hydroxidooxidosulfur radical (HOSO•)-a key intermediate in SO2 photochemistry-in interstellar analogous ices of CO and CO2 at 16 K through hydrogen atom transfer (HAT) reactions. Specifically, 266 nm laser photolysis of HOSO• embedded in solid CO ice yields the elusive hydrogen­bonded complexes HCO•···SO2 and HOCO•···SO, and the latter undergoes subsequent HAT to furnish CO2···HOS• under the irradiation conditions. Similar photo-induced HAT of HOSO• in solid CO2 ice leads to the formation of HOCO•···SO2. The HAT reactions of HOSO• in astronomical CO and CO2 ices by forming reactive acyl radicals may contribute to understanding the interplay between the sulfur and carbon ice-grain chemistry in cold molecular clouds and also in the planetary atmospheric chemistry.

Diazophosphane HPN2.

Diazophosphane HPN2, a heavy analogue of hydrazoic acid (HN3), has been synthesized at low temperature (10 K) through photolytic reactions of molecular nitrogen (N2) with phosphine (PH3) and phosphaketene (HPCO) under irradiations at 193 and 365 nm, respectively. The characterization of HPN2 and its isotopologues DPN2 and HP15N2 by matrix-isolation IR and UV-vis spectroscopy is supported by quantum chemical calculations at the CCSD(T)-F12a/cc-pVTZ-F12 level of theory. Upon irradiation at 266 nm, the P-N bond in HPN2 breaks, whereas its photolysis at 193 nm generates the elusive phosphinyl radical •PN2.

Bimetallic Alloys b-AsxP1-x at High Concentration Differences: Ideal for Photonic Devices.

Black arsenic phosphorus (b-AsxP1-x) is expected to be one of the primary materials for future photonic devices. However, the x-factor is randomly estimated and applied in photonic devices in current studies, rather than systematically analyzing it for a comprehensive understanding. Herein, AsxP1-x switches from a direct band gap semiconductor to an indirect band gap one at x = 0.75. AsxP1-x at x ≤ 0.25 is capable of broadband absorption, while b-AsxP1-x at x ≥ 0.75 can only absorb at specific wavelengths in the perspective of the electron energy transition. Additionally, the optoelectronic response of the integral field-effect transistor configurations constructed with b-AsxP1-x is investigated systematically as a photodetector device. The photonic response characteristics show high polarization sensitivity at x ≥ 0.75, but a typical circuit system signal at x ≤ 0.25. These results suggest that b-AsxP1-x with high concentration differences is a perfect candidate for photonic material.

Intramolecular charge transfer excitation induced by CH3O substitution in the 3-methoxy-1-propoxy radical.

The oxy-substituted alkoxy radicals are generated from the oxidation of ethers. Their degradation path affects ozone production and the formation of the secondary organic aerosol in the atmosphere. In this work, three alkoxy radicals with methoxy (CH3O) substitution at ß, γ, and δ carbon are studied using laser-induced fluorescence (LIF) spectroscopy and theoretical calculation methods. A charge transfer (CT) excited state induced by the CH3O substitution is identified to be because of the intramolecular electron transfer from the C-O-C p orbital to the radical O p orbital. Comparison of the structure and CT transition strength between GGt and TTt conformers of the 3-methoxy-1-propoxy radical (CH3OCH2CH2CH2O) suggests that this long-range charge transfer effect is mainly a through-bond interaction. The CT excited state of CH3OCH2CH2CH2O has a conical intersection with the CO σ → O p excited state, which, hence, changes the LIF spectrum of the radical. Only the decomposition product HCHO was observed in the LIF spectrum of ß substituted radical CH3OCH2CH2O. For δ substituted radical CH3OCH2CH2CH2CH2O, the substitution effect on the radical stability is negligible and its LIF spectrum is close to that of unsubstituted alkoxy radicals. The results provide information for understanding the degradation chemistry of oxygenated hydrocarbon molecules in the atmosphere.

Direct observation of the intermediate radical in the photodissociation of 1,3-cyclohexane dinitrite.

A two-step photodissociation mechanism was proposed in the literature for dinitrites in the absence of direct evidence of the intermediate species. In this work, photodissociation dynamics of cis and trans 1,3-cyclohexane dinitrites are investigated by laser-induced fluorescence (LIF) spectroscopy and theoretical calculation methods. Observation of the fluorescence spectra of the 3-nitrosooxy cyclohexoxy radical provides direct experimental evidence that the intermediate species exists. The results indicate that photodissociation of dinitrites indeed follows a two-step mechanism, i.e. one of the O-NO bonds of the molecule breaks first upon 355 nm laser photolysis and generates an alkoxy radical (RO) plus NO; the alkoxy radical further dissociates in the secondary dissociation step and produces small fragments such as vinoxy etc.

Dispersive Plasmon Damping in Single Gold Nanorods by Platinum Adsorbates.

Surface modifications of plasmonic nanoparticles with metal adsorbates are essential in applications such as plasmonic sensing, plasmon-enhanced photocatalysis, etc., where spectral broadening is usually observed. A single particle study is presented on plasmon damping by adsorption of platinum (Pt) clusters. Single particle dark-field spectroscopy is employed to measure exactly the same gold nanorod before and after the Pt adsorption. The Pt-induced plasmon damping in terms of linewidth increase is found dependent on the resonance wavelength of the measured nanorod, which is dispersive in nature. The measured dispersion generally matches the theoretical prediction, and it basically exhibits a gradual increase with decreasing resonance energy. This increase can be attributed to the fact that the nanorod as a better resonator is more susceptible to the Pt adsorption than the spherical particles. Moreover, simulated results based on discrete dipole approximation method further indicate that the damping is mainly contributed from the adsorbates on the ends of the nanorod and independent on the type of the metal adsorbed. Knowledge and insights gained in this study can be very important for the design and fabrication of plasmonic heterostructures as functional nanomaterials.

Direct coating of mesoporous titania on CTAB-capped gold nanorods.

We demonstrate a CTAB-templated approach towards direct coating of mesoporous titania on gold nanorods in aqueous solutions. The formation of the mesoporous shell is found to be closely correlated with CTAB concentration and the amount of the titania precursor. This approach can be readily extended to form mesoporous titania shells on other CTAB-capped nanoparticles.

Rapid Seedless Synthesis of Gold Nanoplates with Microscaled Edge Length in a High Yield and Their Application in SERS.

We report a facile and reproducible approach toward rapid seedless synthesis of single crystalline gold nanoplates with edge length on the order of microns. The reaction is carried out by reducing gold ions with ascorbic acid in the presence of cetyltrimethylammonium bromide (CTAB). Reaction temperature and molar ratio of CTAB/Au are critical for the formation of gold nanoplates in a high yield, which are, respectively, optimized to be 85 °C and 6. The highest yield that can be achieved is 60 % at the optimized condition. The synthesis to achieve the microscaled gold nanoplates can be finished in less than 1 h under proper reaction conditions. Therefore, the reported synthesis approach is a time- and cost-effective one. The gold nanoplates were further employed as the surface-enhanced Raman scattering substrates and investigated individually. Interestingly, only those adsorbed with gold nanoparticles exhibit pronounced Raman signals of probe molecules, where a maximum enhancement factor of 1.7 × 107 was obtained. The obtained Raman enhancement can be ascribed to the plasmon coupling between the gold nanoplate and the nanoparticle adsorbed onto it.