Thin Copper Plate Defect Detection Based on Lamb Wave Generated by Pulsed Laser in Combination with Laser Heterodyne Interference Technique.

Thin copper plate is widely used in architecture, transportation, heavy equipment, and integrated circuit substrates due to its unique properties. However, it is challenging to identify surface defects in copper strips arising from various manufacturing stages without direct contact. A laser ultrasonic inspection system was developed based on the Lamb wave (LW) produced by a laser pulse.

High-Sensitivity Differential Helmholtz Photoacoustic System Combined with the Herriott Multipass Cell and Its Application in Seed Respiration.

A highly sensitive photoacoustic detection system using a differential Helmholtz resonator (DHR) combined with a Herriott multipass cell is presented, and its implementation to sub-ppm level carbon dioxide (CO) detection is demonstrated. Through the utilization of erbium-doped optical fiber amplifier (EDFA), the laser power was amplified to 150 mW. Within the multipass cell, a total of 22 reflections occurred, contributing to an impressive 33.

Accurate Kinetic Studies of OH + HO Radical-Radical Reaction through Direct Measurement of Precursor and Radical Concentrations with High-Resolution Time-Resolved Dual-Comb Spectroscopy.

The radical-radical reaction between OH and HO has been considered for a long time as an important reaction in tropospheric photochemistry and combustion chemistry. However, a significant discrepancy of an order of magnitude for rate coefficients of this reaction is found between two recent experiments. Herein, we investigate the reaction OH + HO via direct spectral quantification of both the precursor (HO) and free radicals (OH and HO) upon the 248 nm photolysis of HO using infrared two-color time-resolved dual-comb spectroscopy.

A Coin-Sized Oxygen Laser Sensor Based on Tunable Diode Laser Absorption Spectroscopy Combining a Toroidal Absorption Cell.

Laser gas sensors with small volume and light weight are in high demand in the aerospace industry. To address this, a coin-sized oxygen (O) sensor has been successfully developed based on a small toroidal absorption cell design. The absorption cell integrates a vertical-cavity surface-emitting laser (VCSEL) and photodetector into a compact unit, measuring 90 × 40 × 20 mm and weighing 75.

Peroxy radical chemistry during ozone photochemical pollution season at a suburban site in the boundary of Jiangsu-Anhui-Shandong-Henan region, China.

Ambient peroxy radical (RO = HO + RO) concentrations were measured at a suburban site in a major prefecture-level city (Huaibei) in the boundary of Jiangsu-Anhui-Shandong-Henan region, which is the connecting belt of air pollution in the Beijing-Tianjin-Hebei region and the Yangtze River Delta. Measurements were carried out during the period of September to October 2021 to elucidate the formation mechanism of O pollution. The observed maximum concentration of peroxy radicals was 73.

Photophysical oxidation of HCHO produces HO radicals.

Formaldehyde, HCHO, is the highest-volume carbonyl in the atmosphere. It absorbs sunlight at wavelengths shorter than 330 nm and photolyses to form H and HCO radicals, which then react with O to form HO. Here we show HCHO has an additional HO formation pathway.

Rate constant and branching ratio of the reaction of ethyl peroxy radicals with methyl peroxy radicals.

The cross-reaction of ethyl peroxy radicals (CHO) with methyl peroxy radicals (CHO) (R1) has been studied using laser photolysis coupled to time resolved detection of the two different peroxy radicals by continuous wave cavity ring down spectroscopy (cw-CRDS) in their AÃ-X̃ electronic transition in the near-infrared region, CHO at 7602.25 cm, and CHO at 7488.13 cm.

Dimeric Product of Peroxy Radical Self-Reaction Probed with VUV Photoionization Mass Spectrometry and Theoretical Calculations: The Case of CHOOCH.

Organic peroxy radicals (RO) as key intermediates in tropospheric chemistry exert a controlling influence on the cycling of atmospheric reactive radicals and the production of secondary pollutants, such as ozone and secondary organic aerosols (SOA). Herein, we present a comprehensive study of the self-reaction of ethyl peroxy radicals (CHO) by using advanced vacuum ultraviolet (VUV) photoionization mass spectrometry in combination with theoretical calculations. A VUV discharge lamp in Hefei and synchrotron radiation at the Swiss Light Source (SLS) are employed as the photoionization light sources, combined with a microwave discharge fast flow reactor in Hefei and a laser photolysis reactor at the SLS.

Portable cavity ring-down spectrometer for an HO radical measurement: instrument's performance and potential improvement using a narrow linewidth laser.

We report the development of a portable cavity ring-down spectrometer (CRDS) for direct and absolute measurement of HO radical concentration using a distributed feedback (DFB) diode laser operating at 1506 nm. The spectrometer has a compact design with all optics in a 1000 × 400 × 140 mm box. At a pressure of 100 mbar and a ring-down time (τ) of 136 µs, the detection limit of the CRDS spectrometer was ∼ 7.

Cl-Initiated oxidation of methacrolein under NO-free conditions studied by VUV photoionization mass spectrometry.

The Cl-initiated oxidation of methacrolein (MACR, CHO) under NO-free conditions has been investigated in a fast flow tube by using a home-made vacuum ultraviolet (VUV) photoionization mass spectrometer complemented by high-level theoretical calculations. The key species such as intermediates and radicals together with products involved in the oxidation are observed online and confirmed in photoionization mass spectra. The reaction potential energy surfaces of the transient CHO and CHOCl radicals, formed from the hydrogen-abstraction reaction and the addition reaction of MACR with Cl atoms, with oxygen have been theoretically calculated to illuminate the formation of the peroxy radicals of CHOO and CHOClO.

Self-Reaction of Acetonyl Peroxy Radicals and Their Reaction with Cl Atoms.

The rate constant for the self-reaction of the acetonyl peroxy radicals, CHC(O)CHO, has been determined using laser photolysis/continuous wave cavity ring down spectroscopy (cw-CRDS). CHC(O)CHO radicals have been generated from the reaction of Cl atoms with CHC(O)CH, and the concentration time profiles of four radicals (HO, CHO, CHC(O)O, and CHC(O)CHO) have been determined by cw-CRDS in the near-infrared. The rate constant for the self-reaction was found to be = (5.

Data of chemical composition of the particles from OH-initiated oxidation of 1,3,5-trimethylbenzene.

This paper presents the data of chemical composition of the particles from OH oxidation reaction of 1,3,5-trimethylbenzene (1,3,5-TMB). The particle-phase compositions are measured on-line by using a vacuum ultraviolet (VUV) photoionization aerosol mass spectrometer. The assignments of the major peaks of photoionization mass spectrum, as well as their molecular structures, are presented.

Reaction kinetics of 1,4-cyclohexadienes with OH radicals: an experimental and theoretical study.

This work presents the OH-initiated oxidation kinetics of 1,4-cyclochexadiene (1,4-CHD). The temperature dependence of the reaction was investigated by utilizing a laser flash photolysis flow reactor and laser-induced fluorescence (LPFR/LIF) technique over the temperature range of 295-438 K and a pressure of ∼50 torr. The kinetics of the reaction was followed by measuring the LIF signal of OH radicals near 308 nm.

Vacuum ultraviolet photochemistry of the conformers of the ethyl peroxy radical.

We study the conformers of the ethyl peroxy radical (CHO), the simplest peroxy radical having more than one conformer, by combining synchrotron radiation vacuum ultraviolet (VUV) photoionization mass spectrometry with theoretical calculations. The ethyl peroxy radical is formed in a microwave discharge flow tube through the reaction of the ethyl radical (CH) with oxygen molecules, where CH is generated the hydrogen-abstraction reaction of ethane with fluorine atoms. Two kinds of CH, originating from photoionization of CH and from dissociative photoionization of CHO, whose cation is not stable, have been identified and separated in photoionization mass spectra.

Palm-Sized Laser Spectrometer with High Robustness and Sensitivity for Trace Gas Detection Using a Novel Double-Layer Toroidal Cell.

A palm-sized laser spectrometer has been developed for detecting trace gases based on tunable diode laser absorption spectroscopy in combination with a novel double-layer toroidal cell. With the benefit of a homemade electronic system and compact optical design, the physical dimensions of the sensor are minimized to 24 × 15× 16 cm. A toroidal absorption cell, with 84 reflections in 2 layers for an effective optical path length of 8.

Identifying isomers of peroxy radicals in the gas phase: 1-CHOvs. 2-CHO.

The two isomers of the propylperoxy radical 1-CHO and 2-CHO, together with their individual rotamers, are identified and assigned by threshold photoelectron spectroscopy with the aid of high-level theoretical computations, from which their accurate adiabatic ionization energies are derived. This study paves the way to probing elusive peroxy radicals and their isomers in advanced mass spectrometry analysis of combustion and atmospheric reactions.

Implementation of the toroidal absorption cell with multi-layer patterns by a single ring surface.

We developed a type of toroidal multi-pass cell with multi-layer patterns based on the off-axis model. The effective path length of the original toroidal multi-pass cell is extended several roundtrips in comparison with the single-layer pattern, since the inner surface of the toroidal multi-pass cell is more efficiently utilized. The light pattern has been achieved by using the simple ring surface, which is easy to fabricate.

Threshold photoelectron spectroscopy of the HO radical.

We report a synchrotron radiation vacuum ultraviolet photoionization study of the hydroperoxyl radical (HO), a key reaction intermediate in combustion and atmospheric chemistry as well as astrochemistry, using double imaging photoelectron photoion coincidence spectroscopy. The HO radical is formed in a microwave discharge flow tube reactor through a set of reactions initiated by F atoms in a CH/O/He gas mixture. The high-resolution threshold photoelectron spectrum of HO in the 11 eV-12 eV energy range is acquired without interferences from other species and assigned with the aid of theoretically calculated adiabatic ionization energies (AIEs) and Franck-Condon factors.

Threshold photoelectron spectroscopy of the methoxy radical.

We present here a synchrotron radiation vacuum ultraviolet photoionization study of the simplest alkoxy radical, CHO, a key reaction intermediate in atmospheric and combustion chemistry. A microwave discharge fast flow tube connected to a molecular beam sampling system is employed as a chemical reactor to initiate reactions and generate radicals. The CHO cation from direct ionization of the CHO radical is detected successfully in the photoionization mass spectrum close to its ionization threshold.

Online analysis of gas-phase radical reactions using vacuum ultraviolet lamp photoionization and time-of-flight mass spectrometry.

A home-made vacuum ultraviolet photoionization time-of-flight mass spectrometer has been developed and coupled to an atmospheric simulation chamber operated at atmospheric pressure and to a fast flow tube at low pressure (1-10 Torr). Gas sampling from the simulation chamber is realized directly via a capillary effusive beam, and sampling from the flow tube is via a continuous molecular beam inlet. Both devices are connected simultaneously to the ionization chamber of the mass spectrometer and can be switched in-between within minutes to study gas-phase radical reactions of atmospheric interest in a large range of reaction conditions and reaction times (from milliseconds in the flow tube to hours in the simulation chamber).

Water does not catalyze the reaction of OH radicals with ethanol.

Recent experiments suggested that water catalyzes the reaction of OH radicals with alcohols, while another work showed the opposite result. Here, we resolve this disagreement and show that heterogeneous oxidation systematically biased the work showing the catalytic effect and corroborate that water does not catalyze the reaction of OH with alcohols.

Vacuum ultraviolet photodynamics of the methyl peroxy radical studied by double imaging photoelectron photoion coincidences.

The vacuum ultraviolet photoionization of the methyl peroxy radical, CHO, and unimolecular dissociation of internal energy selected CHO cations were investigated in the 9.7-12.0 eV energy range by synchrotron-based double imaging photoelectron photoion coincidence.