Ronald W. Diesen

Photochemical Recoil Spectroscopy

Abstract : The first successful experiments of Photochemical Recoil Spectroscopy are summarized. Results on Chlorine and NO2 are discussed. (Author)

Mass Spectral Studies of Kinetics behind Shock Waves. I. Thermal Dissociation of Chlorine

The coupling of a shock tube to a time‐of‐flight mass spectrometer for the determination of kinetic data is described whereby analysis is performed every 25 μsec. The rate of dissociation of Cl2 has been measured over the temperature range 1700°—3200°K under essentially isothermal and isobaric conditions with the observed rate constants in fair agreement with those obtained by the spectroscopic technique. The observed temperature dependence is less than predicted by simple collision theory with an apparent activation energy of 41±5 kcal/mole.

Mass Spectral Studies of Kinetics behind Shock Waves. II. Thermal Decomposition of Hydrazine

The decomposition of hydrazine diluted in argon has been studied over the temperature range 1200° to 2500°K and pressure range 0.04 to 0.25 atm using a shock tube coupled to a time‐of‐flight mass spectrometer. The time‐resolved mass spectra (25 μsec) enable the simultaneous identification and determination of N2H4, NH3, N2, H2, and the NH2 radical, the five major species observed. The material balance is within the experimental error (10%) during reaction up to complete decomposition.The primary process in the dissociation of hydrazine is shown to be the rupture of the N–N bond to give NH2 radicals. The observed rate constants for the disappearance of hydrazine are those expected of a unimolecular reaction: N2H4+M→ lim k1N2H4*, N2H4*→ lim k22NH2, at or near the second‐order region where the collisional activation (1) is rate controlling. At the higher temperatures, the results are consistent (within experimental error) with the very simple reaction scheme of Reaction (1) and (2) followed by NH2+NH2→ lim k3NH3+NH, NH+NH→ lim k4aN2H2*→ lim k4bN2+H2. At the lowest temperatures the reaction NH2+N2H4→N2H3+NH3 appears to become important.From the experimental concentrations, a value of k3=2.5×1013 cc/mole−sec (2000∘K) is obtained. An order‐of‐magnitude estimate gives k4∼1014 cc/mole−sec (2000∘K).The decomposition of hydrazine diluted in argon has been studied over the temperature range 1200° to 2500°K and pressure range 0.04 to 0.25 atm using a shock tube coupled to a time‐of‐flight mass spectrometer. The time‐resolved mass spectra (25 μsec) enable the simultaneous identification and determination of N2H4, NH3, N2, H2, and the NH2 radical, the five major species observed. The material balance is within the experimental error (10%) during reaction up to complete decomposition.The primary process in the dissociation of hydrazine is shown to be the rupture of the N–N bond to give NH2 radicals. The observed rate constants for the disappearance of hydrazine are those expected of a unimolecular reaction: N2H4+M→ lim k1N2H4*, N2H4*→ lim k22NH2, at or near the second‐order region where the collisional activation (1) is rate controlling. At the higher temperatures, the results are consistent (within experimental error) with the very simple reaction scheme of Reaction (1) and (2) followed by NH2+NH2→ lim k...

Photochemical Recoil Spectroscopy: Chlorine Spectrum and Scattering Analysis

The measurement and analysis of the velocity distribution of the recoiling chlorine atoms from the laser induced photodissociation of Cl2 at 3471 A using a time‐of‐flight technique is described. The expected velocity distribution is numerically calculated from the experimental geometry by appropriate center‐of‐mass (c.m.)‐laboratory (LAB) coordinate transformations. By making the measurements at moderate densities in the interaction zone, the elastic scattering of Cl atoms by Cl2 molecules is observed. Since scattering angles in c.m. correspond to velocity changes in LAB coordinates, the direct recoil signal must be corrected for the effects of multiple elastic scattering. Careful comparison of expected and observed velocity profiles enables one to deduce directly the energy state of the products, the bond dissociation energy D0 ○, and the rainbow scattering angle. The analysis on Cl2 yields D0 ○ (Cl–Cl)=57.05±0.2 kcal/mole, which is in excellent agreement with the JANAF value of 57.04±0.06 kcal/mole and ...