Transient Infrared Absorption Spectra of Reaction Intermediates Detected with a Step‐scan Fourier‐transform Infrared Spectrometer

Abstract

Our group has utilized a step-scan FTIR spectrometer operating in the absorption mode to characterize transient species in chemical reactions upon photo-irradiation of gaseous mixtures in a multipass White cell. The operational temporal resolution is typically 1-10 ms with spectral resolution 0.1-4 cm -1 , depending on conditions. The acquisition of both ac-and dc-coupled signals enables an extraction of minute changes in the large background signal to attain a typical detectable absorbance variation greater than 11 0 -4 . By consideration of reaction mechanisms and comparison of vibrational wavenumbers, IR intensities, and rotational contours predicted with theoretical calculations, we have assigned IR absorption bands of many important atmospheric free radicals and unstable species including their conformers, such as ClCO, ClSO, ClCS, ClCOOH, CH 3 SO 2 , CH 3 SOO, CH 3 OSO, CH 3 SO, CH 3 OO, CH 3 C(O)OO, CH 2 OO C 6 H 5 CO, C 6 H 5 SO 2 , and C 6 H 5 C(O)OO. The advantages and limitations of this technique to perform spectral and kinetic investigations of transient species in chemical reactions are discussed. (2010-). His main research interests focus on the spectroscopy, kinetics, and ion pumps of the photosynthetic proteins, using various time-resolved approaches including step-scan FTIR, nanosecond-resolved transient absorption, and electrochemical methods. Chiao Tung University. The main research topics pursued concern spectroscopy, kinetics and dynamics of free radicals or unstable species, using diverse methods including step-scan time-resolved FTIR (emission or absorption), matrix isolation using p-H 2 , cavity ringdown, IR-VUV photoionization, and ultrafast lasers. He has identified more than 70 new free radicals, most of which are important in atmospheric, combustion, or planetary chemistry. He has received numerous honors, and was elected asThe step-scan measurements are performed under the master mode of the spectrometer (Thermo Nicolet, NEXUS 870), in which the timing trigger is initiated by the spectrometer. Figure 3 CHEMICAL SOCIETY Fig. 5. Schematic of the White cell. The first and second IR beam paths and the first and second UV photolysis beam paths of the multiply reflected light are shown. Circular dots indicate images of the IR beam at each reflection.

Monitoring the Transient Thermal Infrared Emission of Gold Nanoparticles upon Photoexcitation with a Step-Scan Fourier-Transform Spectrometer

“…Moreover, the detector for monitoring the MALDI process is not sensitive when the temperature is lower than 550 K, hampering the detection of moderate increases in temperature. Alternatively, step-scan FTIR, having duplexity in temporal and spectral capability, is advantageous for detecting the transient infrared emission, which could reflect the temperature evolution.…”

“…In the present work, we intended to quantify the temperature of the gold nanoparticles upon the nanosecond pulsed photoexcitation using infrared emission spectroscopy, which was compared with the observed infrared emission contours of the blackbody radiation. A step-scan Fourier-transform infrared spectrometer was employed to monitor the thermal infrared emission because of its wavenumber multiplexity and temporal resolution within submicroseconds . Previous studies demonstrated that metallic nanostructures having larger absorption portions in the extinction coefficients possess higher photothermal efficiency. , In this work, AuNPs capped with different molecules, namely, citrate, CTAB, and mPEG, and CTAB-capped AuNPs of different sizes were employed to serve as the photoinduced nanoheaters.…”

Infrared Spectroscopic and Kinetic Characterization on the Photolysis of Nitrite in Alcohol-Containing Aqueous Solutions

“…The laser scattering was probed by a photodiode (DET10A/M, Thorlabs, 1 ns rise time) as the trigger for the time-resolved data acquisition. A step-scan Fourier-transform infrared spectrometer (Vertex 80, Bruker) was utilized to collect time-resolved interferograms using the ac/dc coupling method. , Without laser irradiation, the dc-coupled signal from the mercury cadmium telluride (MCT) detector (3.5 ns, KMPV8-0.5-J1/DC, Kolmar Technologies) was sent to a voltage amplifier (SR560, Stanford Research Systems) and coupled by dc. Then the output signal from the SR560 was digitized by an analog-to-digital convertor (20 MHz, 14 bits, Bruker) for further calculation of the background spectrum ( S 0 (ν̅)) and for phase correction.…”

Infrared Emission from Photodissociation of Methyl Formate [HC(O)OCH3] at 248 and 193 nm: Absence of Roaming Signature

“…To acquire time-resolved IR emission spectra, we employed a step-scan FTIR spectrometer coupled to a vacuum chamber containing a set of Welsh mirrors to maximize the efficiency of collection of the emission induced from the ultraviolet (UV)-irradiated flowing gaseous samples. Since this system has been described with greater details in previous publications, − only a summary is given here.…”