Richard A. Beyer

Ar+ laser-excited fluorescence of C2 and CN produced in a flame

Fluorescence from C2 and CN has been produced in a CH4/N2O/N2 flame situated within the lasing cavity of an Ar+ laser using several prism-selected laser lines. These transitions have been identified, and fluorescence intensity profiles through the reaction zone of the flame have been obtained. Using the Raman-Stokes Q-branch signal from N2, a temperature profile has also been obtained. These fluorescence profiles have been converted to accurate relative concentration profiles. A rough estimate of absolute concentrations has also been obtained.

Simple burner for laser probing of flames

A research burner for the study of combustion of premixed gases is described. Advantages include access to preheat and primary reaction zones of flames for laser probing, very low heat loss to the burner, and ease of construction. Measurements made with two flame systems to demonstrate performance are reported.

Temperature and concentration profiles in hydrogennitrous oxide flames

Abstract Spontaneous Raman spectroscopy has been used to measure temperature and NO, O 2 , and N 2 concentration profiles in lean to stoichiometric premixed laminar hydrogennitrous oxide flames. Relative concentration profiles for OH were also obtained for these flames by use of laser induced fluorescence. The present NO concentration results for the stoichiometric flame agree with previous NO measurements obtained by a different optical technique. Profiling these species for various equivalence ratios provides a further test for flame modelers.

Kr + and Ar + laser-excited fluorescence of CN in a flame

Laser-excited fluorescence of the CN radical was obtained using various discrete prism selected lines of krypton and argon-ion lasers. The source of hot CN is a slightly rich atmospheric pressure CH4/N2O premixed flame diluted with N2. The flame is placed within the extended cavity of the ion lasers to take advantage of much higher light intensities. Both B2∑+ ← X2∑+ and B2∑+ ← A2Π transitions of CN have been pumped. The Kr+ laser lines, 6764, 6471, 5309, 4680, 4154, 4131, and 3564 A, all pump CN. The 4545-A line of the Ar+ laser also pumps CN. Vibrational and rotational assignments have been made. Detection of CN in a burning propellant sample has been accomplished by this technique.

Polymer induced changes of the crystallization scenario in suspensions of hard sphere like microgel particles

We investigated the crystallization scenario of highly cross linked polystyrene particles dispersed in the good solvent 2-ethylnaphtalene and their mixtures with non-adsorbing low molecular weight polysterene polymer using time resolved static light scattering. The samples were prepared slightly below the melting volume fraction of the polymer free system. For the polymer free samples, we obtained polycrystalline solids via crystallization scenario known from hard sphere suspensions with little competition of wall crystal formation. Addition of non-adsorbing low molecular weight polystyrene polymer leads to a considerably slowing down of the bulk crystallization kinetics. We observed a delay of the precursor to crystal conversion for the bulk crystallization while the induction times for the wall nucleation are reduced. The increased polymer concentration thus shifts the balance between the two competing crystallization pathways giving the possibility to tune the relative amount of wall based crystals.

To make a glass—avoid the crystal

Colloidal model systems allow for a flexible tuning of particle sizes, particle spacings and mutual interactions at constant temperature. Colloidal suspensions typically crystallize as soon as the interactions get sufficiently strong and long-ranged. Several strategies have been successfully applied to avoid crystallization and instead produce colloidal glasses. Most of these amorphous solids are formed at high particle concentrations. This paper shortly reviews experimental attempts to produce amorphous colloidal solids using strategies based on topological, thermodynamic and kinetic considerations. We complement this overview by introducing a (transient) amorphous solid forming in a thoroughly deionized aqueous suspension of highly charged spheres at low salt concentration and very low volume fractions.

From nuclei to micro-structure in colloidal crystallization: Investigating intermediate length scales by small angle laser light scattering.

Hard sphere suspensions are well recognized model systems of statistical physics and soft condensed matter. We here investigate the temporal evolution of the immediate environment of nucleating and growing crystals and/or their global scale distribution using time resolved Small Angle Light Scattering (SALS). Simultaneously performed Bragg scattering measurements provide an accurate temporal gauging of the sequence of events. We apply this approach to studies of re-crystallization in several different shear molten hard sphere and attractive hard sphere samples with the focus being on the diversity of observable signal shapes and their change in time. We demonstrate that depending on the preparation conditions different processes occur on length scales larger than the structural scale, which significantly influence both the crystallization kinetics and the final micro-structure. By careful analysis of the SALS signal evolution and by comparing different suggestions for small angle signal shapes to our data, we can for most cases identify the processes leading to the observed signals. These include form factor scattering from crystals surrounded by depletion zones and structure factor scattering from late stage inter-crystallite ordering. The large variety of different small angle signals thus in principle contains valuable information complementary to that gained from Bragg scattering or microscopy. Our comparison, however, also shows that further refinement and adaptation of the theoretical expressions to the sample specific boundary conditions is desired for a quantitative kinetic analysis of micro-structural evolution.

Raman and fluorescence spectroscopy in a methane-nitrous oxide laminar flame

Using the prism selected lines of argon and krypton lasers, temperature and concentration profiles through the reaction zone of a premixed laminar methane-nitrous oxide flame have been obtained from the Raman signals for N 2 , H 2 O, and CH 4 . Fluorescence signals from NH, OH, CN, and NCO have also been observed. These signals have been assigned to specific pumping transitions where possible, and also converted to relative concentration profiles. Estimates of the absolute concentrations are also determined. The experimentally determined temperatures and species concentrations are compared with thermochemical equilibrium calculations.