David R. Crosley

Laser-induced fluorescence of formaldehyde hot bands in flames.

Laser-induced fluorescence and excitation spectra of formaldehyde in the A-X 4(1)(0) band at 370 nm are recorded in the primary flame front of a Bunsen flame. An examination of partition functions shows that this excitation can minimize temperature bias for formaldehyde in situ diagnostic measurements.

Laser‐induced fluorescence in the B2Σ+–X2Πi system of OH

Laser‐induced fluorescence in the previously unobserved B‐X system is used to detect the high vibrational levels of ground state OH generated by the reaction of H and O3. Light (220–240 nm) from a frequency‐doubled tunable dye laser excites the (0,8), (0,9) and (1m8) vibrational band of the B‐X system. The B state then fluoresces predominantly to the A2Σ+ state beween 400 and 600 nm. Weaker fluorescence to the X state is also observed. From the temporal evolution of the fluorescence, lifetimes are extracted for different vibrational, rotational, and fine‐structure levels of the B state. Large variations are observed between these levels indicating an unexpected predissociation.

Collisional quenching and energy transfer in NS B2Π

Measurements of the collisional removal and vibrational energy transfer rate constants for a series of vibrational levels of the NS B2Π electronic state show surprising specificity on both collider and vibrational level. Total removal rate constants are obtained from the time resolved decay of fluorescence following pulsed laser excitation of v’=4–7 in the presence of collider in a room temperature discharge flow. For CO2, N2O, SF6, and N2 as collision partners, the rate constants double from v’=0 to 1, are a minimum at v’=4, increase at 5, decrease at 6, and increase at 7. In constrast, the rate constants for O2 and H2 increase nearly monotonically with v’. Fluorescence dispersed through a monochromator provides a measure of the vibrational relaxation within the B state. A significant amount of Δv=2 transfer is observed for the three polyatomic colliders.

Flame Chemiluminescence Rate Constants for Quantitative Microgravity Combustion Diagnostics

Absolute excited state concentrations of OH(A), CH(A), and C2(d) were determined in three low pressure premixed methane-air flames. Two dimensional images of chemiluminescence from these states were recorded by a filtered CCD camera, processed by Abel inversion, and calibrated against Rayleigh scattering, Using a previously validated 1-D flame model with known chemistry and excited state quenching rate constants, rate constants are extracted for the reactions CH + O2 (goes to) OH(A) + CO and C2H + O (goes to) CH(A) + CO at flame temperatures. Variations of flame emission intensities with stoichiometry agree well with model predictions.