The Thermal Decomposition of NH2and NH Radicals

Progress and Prospective of Nitrogen-Based Alternative Fuels

Alternative fuels are essential to enable the transition to a sustainable and environmentally friendly energy supply. Synthetic fuels derived from renewable energies can act as energy storage media, thus mitigating the effects of fossil fuels on environment and health. Their economic viability, environmental impact, and compatibility with current infrastructure and technologies are fuel and power source specific. Nitrogen-based fuels pose one possible synthetic fuel pathway. In this review, we discuss the progress and current research on utilization of nitrogen-based fuels in power applications, covering the complete fuel cycle. We cover the production, distribution, and storage of nitrogen-based fuels. We assess much of the existing literature on the reactions involved in the ammonia to nitrogen atom pathway in nitrogen-based fuel combustion. Furthermore, we discuss nitrogen-based fuel applications ranging from combustion engines to gas turbines, as well as their exploitation by suggested end-uses. Thereby, we evaluate the potential opportunities and challenges of expanding the role of nitrogen-based molecules in the energy sector, outlining their use as energy carriers in relevant fields.

Single-tone mid-infrared frequency modulation spectroscopy for sensitive detection of transient species

A single-tone mid-infrared frequency modulation (MIR-FM) spectrometer consisting of a cw-OPO-based laser system, a 500 MHz LiTaO ₃ electro-optical modulator (EOM), and a high-bandwidth GaAs mid-infrared detector has been developed. In order to assess the instrument's sensitivity and time resolution, FM spectra of selected CH ₄ transitions around 3070 cm ^-1 were measured and the reaction Cl + CH ₄ following the 193 nm excimer laser photolysis of oxalyl chloride was investigated by recording concentration-time profiles of HCl at 2925.90 cm ^-1 in a low-pressure slow-flow reactor. Furthermore, OH radicals were generated by UV photolysis of H ₂O ₂ and its transients were recorded at 3447.27 cm ^-1. The minimal detectable absorption of the spectrometer was determined to be A _min=4⋅10^-4 (Δ f _BW=1 MHz, ν~=3447 cm ^-1) by using the Allan approach. Mainly due to thermal noise contributions of the easy-to-saturate photodetector, the detection limit is about a factor of 4 above the shot-noise limit. To the best of our knowledge, this work reports the first implementation of a single-tone MIR-FM spectrometer based on an external EOM modulation scheme and its use for the detection of transient molecular species.

Determining the gas composition for the growth of BNNTs using a thermodynamic approach

B₂N molecules are determined to be major nitrogen-containing gas phase precursors for the growth of BNNTs on boron droplets.

High-energy chemistry of formamide: a simpler way for nucleobase formation

The formation of nucleobases from formamide during a high-energy density event, i.e., the impact of an extraterrestrial body into the planetary atmosphere, was studied by irradiation of formamide ice and liquid samples with a high-power laser in the presence of potential catalysts. FTIR spectroscopy, time-resolved emission spectroscopy, and GC-MS were subsequently used to monitor the dissociation of this molecule into stable molecular fragments (HCN, H2O, HNCO, H2, CO, and NH3) and unstable species (HNC, •CN, and •NH). The kinetic and thermodynamic models of the high-energy density event molecular dynamics have been suggested together with the reaction routes leading from the dissociation products to the nucleobases. In addition, using theoretical calculations, we propose a simple new reaction pathway for the formation of both pyrimidine and purine nucleobases involving •CN radical chemistry.

Room Temperature and Shock Tube Study of the Reaction HCO + O2 Using the Photolysis of Glyoxal as an Efficient HCO Source

The rate of the reaction 1, HCO+O2-->HO2+CO, has been determined (i) at room temperature using a slow flow reactor setup (20 mbar<p<500 mbar) and (ii) in the temperature range 739 K<T<1108 K behind reflected shock waves (0.82 bar<p<1.84 bar) employing a perturbation approach. Following the 193 nm excimer laser photolysis of mixtures of glyoxal in Ar, concentration-time profiles were measured using frequency modulation (FM) detection of HCO at a wavelength of lambda=614.752 nm. Observed differences between HCO concentration-time profiles measured with and without O2 added to the reaction mixtures could be almost exclusively attributed to reaction 1. The determined rate constants, k1(295 K)=(3.55+/-0.05)x10(12) cm3 mol-1 s-1, k1(739-1108 K)=3.7x10(13) exp(-13 kJ mol-1/RT) cm3 mol-1 s-1 (Delta log k1=+/-0.16), reveal a slightly positive temperature dependence of reaction 1 at high temperatures. Furthermore, the 193 nm photolysis of glyoxal, (CHO)2, has been proven to be an efficient HCO source. Besides HCO, photolysis of the precursor also produces H atoms. The ratio of initially generated H atoms and HCO radicals, f=[H]0/[HCO]0total, was found to depend on the total density rho. At room temperature, it varies from f=1.6 at rho=8x10(-7) mol cm-3 to f=3.0 at rho=2x10(-5) mol cm-3. H atoms are transformed via reaction 4, H+(CHO)2-->H2+HCO+CO, into additional HCO radicals. The rate constants of reaction 4 were determined from unperturbed photolysis experiments to be k4(295 K)=(3.6+/-0.3)x10(10) cm3 mol-1 s-1 and k4(769-1107 K)=5.4x10(13)exp(-18 kJ mol-1/RT) cm3 mol-1 s-1(Delta log k4=+/-0.12).

Transient laser frequency modulation spectroscopy

Explicitly time-dependent implementations of optical frequency modulation spectroscopy have been recently applied to a wide range of problems in chemical physics. We provide a brief description of the methodology, with an emphasis on its intrinsic advantages for interrogating transient species. Several examples highlight the application of the technique to high-resolution absorption spectra of free radicals, rate measurements for gas-phase reactions, and Doppler spectroscopy of the gas-phase products of photoinitiated reactions.