William R. Anderson

Concentration profiles of NH and OH in a stoichiometric CH4/N2O flame by laser excited fluorescence and absorption

Abstract The concentration profiles of NH and OH were measured in an atmospheric pressure, premixed, laminar CH4/N2O flame over a porous-plug, flat flame burner. Relative profiles were obtained by laser excited fluorescence for both compounds and normalized by laser absorption at a single point for NH. The OH concentration was high enough to allow absorption measurements at several points for comparison with fluorescence results. The steeply rising portions of the profiles occur at about the same height above the burner, but the NH is confined to the primary reaction zone, while the OH decay extends into the burnt gases. The OH decay was analyzed using a simple rate law. The results and comparisons with previous results in CH4/air flames are discussed briefly. Brief studies of the peak NH concentration in CH4/air, CH4/NO, H2/NO and H2/N2O flames were made in order to elucidate the flame chemistry.

Franck–Condon factors for the B–X system of S2

A frequency‐doubled tunable dye laser has been used to selectively excite individual rotational levels within the vibrational levels υ′=2, and 6–9, of the B3Σ−u state of S2. Measurements of the intensity in emission of all the (υ,υ″) bands permit determination of the absolute Franck–Condon factors qv′v″. Combined with previous studies, this work completes the set of qv′v″ for bound–bound transitions within the B–X system. A simple pictorial representation of the Franck–Condon factors is presented, and conclusions may be drawn concerning overlap with the B‐state wave functions above the predissociation limit.

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.

Laser-excited fluorescence in the A—X system of NH

Abstract Laser-excited fluorescence has been observed in a discharge flow system for the A 3 Π i —X 3 ∑ − system of NH. Excitation has been carried out in both the (1,0) band near 3050 A and the (0,0) band near 3360 A. The ratio of transition probabilities for the (0,1) and (0,0) bands is 0.0067 ±0.0012.

Importance of the perpendicular transition leading to ground state atoms in the photodissociation of NaI

Abstract Measurements of the angular distribution of the alkali photofragment from photodissociation of a molecular beam of sodium iodide using linearly polarized light of wavelength 347.1 nm shows that a perpendicular transition from the 1 Σ + ionic ground state to the Ω = 1 covalent excited state accounts for 80 ± 9% of the absorption leading to ground state neutral atoms at that energy.

Lifetimes and quenching of B2Σ+ PO by atmospheric gases

Pulsed laser excited fluorescence in the B 2Σ+ ← X 2π system of gas phase PO was used to measure the lifetime for v’=0 of the B state. Rotationally resolved measurements for a few selected J’ levels, at Ar or He carrier gas pressures of ∼2 Torr, reveal no dependence of the lifetime on the rotational level excited. Earlier measurements of relative fluorescence intensities in the v’=0 vibrational progression were reinterpreted to extract the dependence of the electronic transition moment on internuclear distance. Using this transition moment, no lifetime dependence on rotational level is to be expected, even at low pressures. Rate constants for quenching of the B state PO by N2, O2, CO2, and H2O, and upper limits thereof for He and Ar are reported. O2 was found to react with ground state PO. A crude measurement of the rate constant was performed. The result is compared to two other known measurements. The rate constant is in excellent agreement with the previous measurement, but in poor agreement with that ...

Kr+ laser excitation of NH2 in atmospheric pressure flames

Fluorescence in the A 2A1−X 2B1 system of the NH2 radical has been excited in NH3/N2O/N2, H2/N2O/N2, and CH4/N2O/N2 flames using the 6471 A line of a krypton ion laser. Rotationally resolved fluorescence spectra indicate that the laser simultaneously pumps two rotational lines in the (0,11,0)–(0,2,0)∑ vibrational hot band of the radical. The placement of the laser line relative to the two molecular transitions has been inferred from intensities in the fluroescence spectrum. Rotational and vibrational energy transfer in the excited state were observed to be very slow in comparison to electronic quenching by the flame molecules. An NH2 density profile in a rich H2/N2O/N2 flame is given. Also, a method for the calculation of Einstein coefficients and oscillator strengths for nonperturbed, main‐branch transitions is presented.

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.

Photodissociation of the alkali iodides at 347.1 nm: Experimental angular distributions and dynamic model for their interpretation

The angular distributions of the alkali photofragment resulting from photodissociation of a molecular beam of NaI, KI, CsI, or RbI by a pulsed, linearly polarized laser beam at 347.1 nm have been measured. At the wavelength used, only production of ground state atoms is energetically feasible. The angular distributions indicate a trend in the perpendicular:parallel transition ratio from about 4:1 for NaI to about 2:1 for RbI and CsI. This interpretation assumes Hund’s case (c) coupling and excited states of pure perpendicular or parallel symmetry. A new model was developed to calculate the laboratory distribution from any center of mass distribution, including those resulting from multiphoton or saturated transitions. The individual counting model (ICM) simultaneously takes into account contributions from excited state lifetime, rotational distribution, and translational motion of the molecule. It is concluded that further study of the systems at several wavelengths in the lowest energy absorption band is...

Energy transfer and quenching rates of laser-pumped electronically excited alkalis in flames

A pulsed, tunable dye laser has been used to excite each of the 3p, 3d, 4p, 5s and 4d levels of sodium atoms seeded into an atmospheric pressure acetylene-air flame. Three of these transitions, 3d, 5s and 4d, involve two-photon absorption from the ground 3s state. Fluorescence measurements furnish the populations of each of the levels populated by collisional transfer, enabling the deduction of relative energy transfer and quench rates among the four higher states. Fluorescence and opto-acoustic measurements under conditions near optical saturation of the 3p transition yield energy transfer rates and quenching rates for the two doublet components. Total collision-broadened linewidths are obtained by scanning the laser in a narrow-line mode. A qualitative experiment seeding the flame with both sodium and lithium suggests the presence of electronic-to-vibrational-to-electronic energy transfer.