A Laser-Based Multipass Absorption Sensor for Sub-ppm Detection of Methane, Acetylene and Ammonia

A compact, sensitive laser-based absorption sensor for multispecies monitoring of methane (CH4), acetylene (C2H2) and ammonia (NH3) was developed using a compact multipass gas cell. The gas cell is 8.8 cm long and has an effective optical path length of 3.0 m with a sampling volume of 75 mL. The sensor is composed of three fiber-coupled distributed feedback lasers operating near 1512 nm, 1532 nm and 1654 nm, an InGaAs photodetector and a custom-designed software for data acquisition, signal processing and display. The lasers were scanned over the target absorption features at 1 Hz. First-harmonic-normalized wavelength modulation spectroscopy (f = 3 kHz) with the second harmonic detection (WMS-2f/1f) is employed to eliminate the unwanted power fluctuations of the transmitted laser caused by aerosol/particles scattering, absorption and beam-steering. The multispecies sensor has excellent linear responses (R2 > 0.997) within the gas concentration range of 1–1000 ppm and shows a detection limit of 0.32 ppm for CH4, 0.16 ppm for C2H2 and 0.23 ppm for NH3 at 1 s response time. The Allan–Werle deviation analysis verifies the long-term stability of the sensor, indicating a minimal detection limit of 20–34 ppb were achieved after 60–148 s integration time. Flow test of the portable multispecies sensor is also demonstrated in this work.

Sub-Hz Differential Rotational Spectroscopy of Enantiomers

We demonstrate for the first time high-precision differential microwave spectroscopy, achieving sub-Hz precision by coupling a cryogenic buffer gas cell with a tunable microwave Fabry–Perot cavity. We report statistically limited sub-Hz precision of (0.08 ± 0.72) Hz, observed between enantiopure samples of (R)-1,2-propanediol and (S)-1,2-propanediol at frequencies near 15 GHz. We confirm highly repeatable spectroscopic measurements compared to traditional pulsed-jet methods, opening up new capabilities in probing subtle molecular structural effects at the 10−10 level and providing a platform for exploring sources of systematic error in parity-violation searches. We discuss dominant systematic effects at this level and propose possible extensions of the technique for higher precision.

Thermal analysis of building materials for decoration and INFRARED spectroscopy of gaseous products of their thermal destruction

В настоящей статье представлены результаты экспериментального исследования термической деструкции отделочных строительных материалов и идентификации продуктов их термического разложения. Исследование термической деструкции отделочных строительных материалов осуществлялось методом динамического термогравиметрического анализа, а идентификация продуктов термического разложения отделочных строительных материалов – методом инфракрасной спектроскопии. Термический анализ проводился на приборе синхронного термического анализа NETZSCH STA 449 F3 Jupiter, позволяющем фиксировать изменение массы и величин теплового потока от температуры. Нагрев образцов осуществлялся со скоростью 10℃/мин в атмосфере воздуха с расходом 100 мл/мин в интервале температур 25℃-650℃. Образующиеся при термической деструкции газообразные продукты анализировались на ИК-Фурье спектрометре «ФСМ 1201» с газовой кюветой ТГА 100 при длинах волн 600-4500 см-1. По результатам исследования получены ТГ, ДТГ и ДСК-кривые, характеризующие соответственно потерю массы образца, скорость потери массы и изменение величины теплового потока от температуры, а также ИК-спектры продуктов термической деструкции отделочных строительных материалов при различных температурах. Установлено, что отделочные строительные материалы при их термической деструкции образуют различные химические соединения, отдельные из которых представляют опасность для организма человека. This article presents the results of experimental research on thermal destruction of finishing building materials and a hazard assessment of the process. Thermal destruction of finishing materials was investigated by thermal analysis and the risk of the process was assessed by infrared spectroscopy of gaseous products resulting from thermal destruction. The thermal analysis was carried out by dynamic thermogravimetric analysis on the synchronous thermal analysis instrument NETZSCH STA 449 F3 Jupiter, which makes it possible to detect changes in mass and heat flow from temperature. The heating of the samples was carried out at a rate of 10 ℃/min in the atmosphere with a consumption of 100 ml/min. The gaseous products formed during thermal destruction were analyzed by infrared spectroscopy on IR-Fourier spectrometer «FSM 1201» with gas cell TGA 100 at wavelengths of 600-4500 cm-1. The results of the study led to the production of TG, TFG and DSK curves, describing respectively the loss of sample mass, the rate of mass loss and the change of heat flow from temperature as well as infrared spectra of products of thermal destruction of finishing building materials at various temperatures. It has been found that the finishing building materials, when thermally disrupted, form various chemical compounds, some of which are dangerous to the human body.

A complete data set for the simulation of electron transport through gaseous tetrahydrofuran in the energy range 1–100 $$\hbox {eV}$$

A self-consistent data set, with all the necessary inputs for Monte Carlo simulations of electron transport through gaseous tetrahydrofuran (THF) in the energy range 1–100 eV, has been critically compiled in this study. Accurate measurements of total electron scattering cross sections (TCSs) from THF have been obtained, and considered as reference values to validate the self-consistency of the proposed data set. Monte Carlo simulations of the magnetically confined electron transport through a gas cell containing THF for different beam energies (3, 10 and 70 eV) and pressures (2.5 and 5.0 mTorr) have also been performed by using a novel code developed in Madrid. In order to probe the accuracy of the proposed data set, the simulated results have been compared with the corresponding experimental data, the latter obtained with the same experimental configuration where the TCSs have been measured. Graphic Abstract

Thermal Instabilities and Shattering in the High-redshift WHIM: Convergence Criteria and Implications for Low-metallicity Strong H i Absorbers

Using a novel suite of cosmological simulations zooming in on a megaparsec-scale intergalactic sheet (pancake) at z ∼ (3–5), we conduct an in-depth study of the thermal properties and H i content of the warm-hot intergalactic medium (WHIM) at those redshifts. The simulations span nearly three orders of magnitude in gas cell mass, ∼(7.7 × 106–1.5 × 104)M ⊙, one of the highest-resolution simulations of such a large patch of the intergalactic medium (IGM) to date. At z ∼ 5, a strong accretion shock develops around the pancake. Gas in the postshock region proceeds to cool rapidly, triggering thermal instabilities and generating a multiphase medium. We find the mass, morphology, and distribution of H i in the WHIM to all be unconverged, even at our highest resolution. Interestingly, the lack of convergence is more severe for the less-dense, metal-poor intrapancake medium (IPM) in between filaments and far outside galaxies. With increased resolution, the IPM develops a shattered structure with most of the H i in kiloparsec-scale clouds. From our lowest-to-highest resolution, the covering fraction of metal-poor (Z < 10−3 Z ⊙) Lyman-limit systems (N H I > 1017.2cm−2) in the z ∼ 4 IPM increases from ∼(3–15)%, while that of metal-poor damped Lyα absorbers (N H I > 1020cm−2) increases from ∼(0.2–0.6)%, with no sign of convergence. We find that a necessary condition for the formation of a multiphase shattered structure is resolving the cooling length, l cool = c s t cool, at T ∼ 105 K. If this is unresolved, gas “piles up” at T ≲ 105 K and further cooling becomes very inefficient. We conclude that state-of-the-art cosmological simulations are still unable to resolve the multiphase structure of the WHIM, with potentially far-reaching implications.

Evaluation of Recommended Cross Sections for the Simulation of Electron Tracks in Water

The accuracy of the most recent recommended cross sections dataset for electron scattering from gaseous H2O (J. Phys. Chem. Ref. Data 2021, 50, 023103) is probed in a joint experimental and computational study. Simulations of the magnetically confined electron transport through a gas cell containing H2O for different beam energies (3, 10 and 70 eV) and pressures (2.5 to 20.0 mTorr) have been performed by using a specifically designed Monte Carlo code. The simulated results have been compared with the corresponding experimental data as well as with simulations performed with Geant4DNA. The comparison made between the experiment and simulation provides insight into possible improvement of the recommended dataset.