Oliver C. Fleischmann

Bio: Oliver C. Fleischmann is an academic researcher from University of Bremen. The author has contributed to research in topics: Absorption spectroscopy & Fourier transform spectroscopy. The author has an hindex of 4, co-authored 5 publications receiving 759 citations.

Measurements of molecular absorption spectra with the SCIAMACHY pre-flight model: instrument characterization and reference data for atmospheric remote-sensing in the 230–2380 nm region

Abstract: Using the scanning imaging absorption spectrometer for atmospheric chartography (SCIAMACHY) pre-flight model satellite spectrometer, gas-phase absorption spectra of the most important atmospheric trace gases (O3, NO2, SO2, O2, OClO, H2CO, H2O, CO, CO2, CH4, and N2O) have been measured in the 230–2380 nm range at medium spectral resolution and at several temperatures between 203 and 293 K. The spectra show high signal-to-noise ratio (between 200 up to a few thousands), high baseline stability (better than 10−2) and an accurate wavelength calibration (better than 0.01 nm) and were scaled to absolute absorption cross-sections using previously published data. The results are important as reference data for atmospheric remote-sensing and physical chemistry. Amongst other results, the first measurements of the Wulf bands of O3 up to their origin above 1000 nm were made at five different temperatures between 203 and 293 K, the first UV-Vis absorption cross-sections of NO2 in gas-phase equilibrium at 203 K were recorded, and the ultraviolet absorption cross-sections of SO2 were measured at five different temperatures between 203 and 296 K. In addition, the molecular absorption spectra were used to improve the wavelength calibration of the SCIAMACHY spectrometer and to characterize the instrumental line shape (ILS) and straylight properties of the instrument. It is demonstrated that laboratory measurements of molecular trace gas absorption spectra prior to launch are important for satellite instrument characterization and to validate and improve the spectroscopic database.

New ultraviolet absorption cross-sections of BrO at atmospheric temperatures measured by time-windowing Fourier transform spectroscopy

Abstract: The UV absorption cross-section spectra of the atmospherically important radical BrO have been determined using the recently developed technique of time-windowing Fourier transform spectroscopy (TW-FTS). The absorption spectra of the A 2 Π 3/2 – X 2 Π 3/2 band system were recorded in the flash photolysis of a gaseous mixture of Br2 and O3. The bromine-photosensitized decomposition of O3 was observed at five different temperatures between 203 and 298 K. The absolute UV absorption cross-section was determined from the time-dependent observation of reactant and product absorptions and by a kinetic analysis of the BrO behavior. The integrated UV absorption cross-section of BrO was, within the accuracy of the measurements, constant over the temperature range studied, as expected from spectroscopic considerations. For the (7, 0) vibrational band at 29 540 cm−1 (338.5 nm), the peak absorption cross-sections were determined to be 2.19±0.23 at 298 K, 2.23±0.23 at 273 K, 2.52±0.26 at 243 K, 2.75±0.29 at 223 K, and 3.03±0.31 at 203 K (all in units ×10−17 cm2 per molecule, at a spectral resolution of 3.8 cm−1, with error intervals of 2σ). Further, vibrational constants and the dissociation limit for the electronic state A 2 Π 3/2 were derived. The A←X dissociation energy was determined to be D 0 =35 240±160 cm−1 or 421.6±1.9 kJ/mol.

Time-windowing Fourier transform absorption spectroscopy for flash photolysis investigations

Abstract: A technique for recording time-resolved absorption spectra using a commercial continuous-scan Fourier transform spectrometer (FTS) is presented. The method has been designed for the observation of experiments at temporal resolutions from 10 −4 to 10 −2 s, with delays longer than a second between two experimental repetitions. This is accomplished by synchronizing the observed experiment to certain positions of the interferometer scanning mirror. Unlike other interleaving or stroboscopic techniques, a trigger is not generated for every interferogram point. Instead, time windows are used that are several interferogram points wide. For experiments with a low repetition rate (0.1–1 Hz), the approach has advantages concerning measurement time and spectral resolution when compared to the step-scan and to fast synchronized continuous-scan methods. The time-windowing Fourier transform spectrometer (TW-FTS) has been implemented as a hardware and software add-on to a commercial continuous-scan Michelson interferometer. No changes were made to the instrument. Two validation experiments were carried out by observing the formation and self-reaction of BrO after the flash photolysis of a Br 2 /O 3 mixture at 298 K. The experimental concentration–time profiles were in good agreement with decay curves from a chemical kinetics simulation of the experiments. Further, a UV absorption spectrum of BrO, recorded by the TW-FTS method, had a comparable quality as a static FTS recording.

The visible absorption spectrum of OBrO, investigated by Fourier transform spectroscopy.

Abstract: By the utilization of a new laboratory method to synthesize OBrO employing an electric discharge, the visible absorption spectrum of gaseous OBrO has been investigated. Absorption spectra of OBrO have been recorded at 298 K, using a continuous-scan Fourier transform spectrometer at a spectral resolution of 0.8 cm-1. A detailed vibrational and rotational analysis of the observed transitions has been carried out. The FTS measurements provide experimental evidence that the visible absorption spectrum of OBrO results from the electronic transition C(2A2)−X(2B1). Vibrational constants have been determined for the C(2A2) state (ω1 = 648.3 ± 1.9 cm-1 and ω2 = 212.8 ± 1.2 cm-1) and for the X(2B1) state (ω1 = 804.1 ± 0.8 cm-1 and ω2 = 312.2 ± 0.5 cm-1). The vibrational bands (1,0,0), (2,0,0), and (1,1,0) show rotational structure, whereas the other observed bands are unstructured because of strong predissociation. Rotational constants have been determined experimentally for the upper electronic state C(2A2). By mo...

The Visible Absorption Spectrum of OBrO, Investigated by Fourier Transform Spectroscopy.

Abstract: By the utilization of a new laboratory method to synthesize OBrO employing an electric discharge, the visible absorption spectrum of gaseous OBrO has been investigated. Absorption spectra of OBrO have been recorded at 298 K, using a continuous-scan Fourier transform spectrometer at a spectral resolution of 0.8 cm-1. A detailed vibrational and rotational analysis of the observed transitions has been carried out. The FTS measurements provide experimental evidence that the visible absorption spectrum of OBrO results from the electronic transition C(2A2)−X(2B1). Vibrational constants have been determined for the C(2A2) state (ω1 = 648.3 ± 1.9 cm-1 and ω2 = 212.8 ± 1.2 cm-1) and for the X(2B1) state (ω1 = 804.1 ± 0.8 cm-1 and ω2 = 312.2 ± 0.5 cm-1). The vibrational bands (1,0,0), (2,0,0), and (1,1,0) show rotational structure, whereas the other observed bands are unstructured because of strong predissociation. Rotational constants have been determined experimentally for the upper electronic state C(2A2). By mo...

The HITRAN 2008 molecular spectroscopic database

Abstract: This paper describes the contents of the 2016 edition of the HITRAN molecular spectroscopic compilation. The new edition replaces the previous HITRAN edition of 2012 and its updates during the intervening years. The HITRAN molecular absorption compilation is composed of five major components: the traditional line-by-line spectroscopic parameters required for high-resolution radiative-transfer codes, infrared absorption cross-sections for molecules not yet amenable to representation in a line-by-line form, collision-induced absorption data, aerosol indices of refraction, and general tables such as partition sums that apply globally to the data. The new HITRAN is greatly extended in terms of accuracy, spectral coverage, additional absorption phenomena, added line-shape formalisms, and validity. Moreover, molecules, isotopologues, and perturbing gases have been added that address the issues of atmospheres beyond the Earth. Of considerable note, experimental IR cross-sections for almost 300 additional molecules important in different areas of atmospheric science have been added to the database. The compilation can be accessed through www.hitran.org. Most of the HITRAN data have now been cast into an underlying relational database structure that offers many advantages over the long-standing sequential text-based structure. The new structure empowers the user in many ways. It enables the incorporation of an extended set of fundamental parameters per transition, sophisticated line-shape formalisms, easy user-defined output formats, and very convenient searching, filtering, and plotting of data. A powerful application programming interface making use of structured query language (SQL) features for higher-level applications of HITRAN is also provided.

Direct Kinetic Measurements of Criegee Intermediate (CH2OO) Formed by Reaction of CH2I with O2

Abstract: Ozonolysis is a major tropospheric removal mechanism for unsaturated hydrocarbons and proceeds via "Criegee intermediates"--carbonyl oxides--that play a key role in tropospheric oxidation models. However, until recently no gas-phase Criegee intermediate had been observed, and indirect determinations of their reaction kinetics gave derived rate coefficients spanning orders of magnitude. Here, we report direct photoionization mass spectrometric detection of formaldehyde oxide (CH(2)OO) as a product of the reaction of CH(2)I with O(2). This reaction enabled direct laboratory determinations of CH(2)OO kinetics. Upper limits were extracted for reaction rate coefficients with NO and H(2)O. The CH(2)OO reactions with SO(2) and NO(2) proved unexpectedly rapid and imply a substantially greater role of carbonyl oxides in models of tropospheric sulfate and nitrate chemistry than previously assumed.

The libRadtran software package for radiative transfer calculations (version 2.0.1)

Abstract: . libRadtran is a widely used software package for radiative transfer calculations. It allows one to compute (polarized) radiances, irradiance, and actinic fluxes in the solar and thermal spectral regions. libRadtran has been used for various applications, including remote sensing of clouds, aerosols and trace gases in the Earth's atmosphere, climate studies, e.g., for the calculation of radiative forcing due to different atmospheric components, for UV forecasting, the calculation of photolysis frequencies, and for remote sensing of other planets in our solar system. The package has been described in Mayer and Kylling (2005). Since then several new features have been included, for example polarization, Raman scattering, a new molecular gas absorption parameterization, and several new parameterizations of cloud and aerosol optical properties. Furthermore, a graphical user interface is now available, which greatly simplifies the usage of the model, especially for new users. This paper gives an overview of libRadtran version 2.0.1 with a focus on new features. Applications including these new features are provided as examples of use. A complete description of libRadtran and all its input options is given in the user manual included in the libRadtran software package, which is freely available at http://www.libradtran.org .