Interferogram co-adding

The growth and decay of all other species (including O3) were monitored by Fourier transform infrared (FT-IR) spectroscopy at a total pathlength of 460 meters and a spectral resolution of 1 cm". At this pathlength, the intense absorptions of H2O and CO limit the usable IR spectral windows to the approximate regions 750-1300, 2000-2300, and 2400-3000 cm". Each spectrum (700-3000 cm" ) was adequately covered by the response of the Cu Ge detector. Approximately 40 seconds were required to collect the 32 interferograms co-added for each spectrum. 

Figure 2 Light-induced FTIR difference spectra of Rps. viridis RC between a) P+QA and PQA. lOOK, 112 640 interferograms co-added b) P+QaQB- and PQaQB, 290K,...

Transmission infrared spectra of species adsorbed on the catalyst were taken with a Digilab FTS-10M Fourier-transform infrared spectrometer, using a resolution of 4 cm-l. To improve the signal-to-noise ratio, between 10 and 100 interferograms were co-added. Spectra of the catalyst taken following reduction in H2 were subtracted from spectra taken in the presence of NO to eliminate the spectrum of the support. Because of the very short optical path through the gas in the reactor and the low NO partial pressures used in these studies, the spectrum of gas-phase NO was extremely weak and did not interfere with the observation of the spectrum of adsorbed species. 

A modified out-of-compartment IRE holder (SPECAC) that could be configured as a 125 pi flow cell was used for this study. The IREs used here measure 72x10x6 mm they have a 45° angle of incidence, and 7 internal reflections. Interferograms were collected on a Nicolet 800 FTIR spectrometer equipped with a liquid nitrogen cooled MCT detector. For each spectmm, 1000 interferograms were co-added at 4 cm resolution (total collection time 6 minutes). Duplicate data sets were collected on Ge and ZnSe IREs. For each spectmm, 500-1000 pi of a 3 or 30mg/ml protein solution (20 mM phosphate, pH 7.0) were used. The protocol developed for the collection of solution spectra is summarized in Table I. 

IR speetra were recorded at a spectral resolution of 1 cm . Between 8 and 12 spectra were recorded in each kinetic experiment, every spectrum comprised of 128 co-added interferograms. Before the kinetic experiment a series of five experiments were performed for every nitrocresol compound in order to obtain the photolysis and wall loss rates. These latter two constants were used in corrections of the OH kinetic rate data. Formation of OH radicals was observed during the photolysis of nitrocresols. Using isoprene as scavenger for OH radicals (kon = 1.0 x lO cm s, Atkinson and Arey, 2003) it was possible to calculate the eoneentration of OH radicals produced by the photolysis and flius calculate a correct rate eonstant for the photolysis frequency. 

PfRhSn02/C nanoparticle catalyst (b) in a 0.2 M ethanol in 0.1 M HCIO4 solution. 128 interferograms (resolution 8 cm" ) were collected and co-added into each spectrum [70]... 

Figure 3 a) Series of time-resolved FTIR difference spectra of Rb. sphaeroides RC (40% Qb) at 280K each separated by 185 ms. Data for each value of t consists of 1 540 co-added interferograms. The spectrum at t=0 is recorded under illumination (100 msec). The background spectrum at t=-185 msec shows the level of S/N obtained for the measurements b) Changes in amplitude at several wavenumbers as a function of time. The solid line is the least-squares fit of the data in Fig.3a according to the bi-exponential function ... 

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