R. F. Heidner

Absolute rate coefficients for F+H2 and F+D2 at T=295–765 K.

The rate coefficients of the F+H2 and F+D2 reactions must be accurately known over a wide temperature range if the HF and DF chemical lasers are to be properly modeled. Although the pulsed and cw chemical lasers operate at elevated temperatures (500 to 2000 K), no absolute rate data exist for T≳400 K. Extension of the infrared multiphoton dissociation–infrared fluorescence technique permitted the following Arrhenius equations to be determined between 295 and 765 K: kF+H2=(1.3±0.25)×1014 exp[−(1182±100)/RT]; kF+D2=(6.4±2.2)×1013 exp [−(1200±142)/RT]; kF+H2/kF+D2=(2.1±0.8) exp[(18±250)/RT].

Temperature dependence of O2(1Δ)+O2(1Δ) and I(2P1/2)+O2(1Δ) energy pooling

The electronic‐energy pooling reactions forming O2(1Σ) are of critical importance to the overall mechanism of the O2(1Δ)–I atom transfer laser. In this study, we report temperature‐dependent rate coefficient data for O2(1Δ)+O2(1Δ)→k2O2(1Σ)+O2(3Σ) and O2(1Δ)+I(2P1/2)→k3O2(1Σ)+I. These data were obtained using a temperature‐controlled kinetic flow tube equipped with computer‐controlled spectroscopic diagnostics. The fundamental data reported are k2(T)/k2(295) = (3.5±1.5)exp(−780/RT) and k3(T)/k2(T) = (5.5±1.0)×103. Both rate‐coefficient ratios are reported for the temperature range T = 259 to 353 K. The results are compared with earlier measurements of these processes.

The vibrational deactivation of HF(v=3) and HF(v=2) by H atoms

The rate of HF(v=2 and 3) removal by H atoms was measured at T=295 K. The measurements were performed by laser‐induced fluorescence in a discharge flow tube in which H atoms were produced by a microwave discharge. The absolute H‐atom concentrations were measured by isothermal calorimetry with a Pt wire coil as a catalytic probe. A small fraction of the injected HF(v=0) was pumped first to HF(v=1) and subsequently to HF(v=2) and HF(v=3) by the multiline output from a pulsed HF transverse excitation atmospheric (TEA) laser. The exponential decay times of the HF 3–0 fluorescence with and without the microwave discharge and the measured H‐atom concentrations were used to calculate a removal rate of 6.3×1013 cm3/mol‐sec for HF(v=3). This rate is ∼400 times faster than the deactivation of HF(v=1) by H atoms and ∼100 times faster than the deactivation of HF(v=2) also reported in this study. Thus, it many account for the low laser output from the higher vibrational levels that has been observed in pulsed HF laser...

Vibrational deactivation of HF(v=1) and DF(v=1) by H and D atoms

The deactivation of HF(v=1) and DF(v=1) by H and D atoms was studied at 295 K by means of the techniques of laser‐induced infrared fluorescence and isothermal calorimetry. The upper limits for the deduced rate coefficients are well‐defined, but the lower limits are imprecise. The results of this study are compared with other experimental data and with trajectory calculations. Qualitative data are presented regarding the role of reactive, i.e., F‐atom exchange, versus nonreactive collisions in the removal of the v=1 level. A verification of the method was made by determining a rate coefficient for H+HCl(v=1) that is in good agreement with a recent study.

Dissociation of I2in O2(1Δ)-I atom transfer lasers

Abstract The dissociation of I 2 in the O 2 ( 1 Δ)-I atom transfer laser is shown to result from collisions with a species other than O 2 ( 1 Σ). The interaction of O 2 ( 1 Δ) with low-lying electronic states of I 2 is discussed.

Kinetic study of H+HF(v=3): Kinetic isotope effect and temperature dependence

Rates of HF(v = 3) removal by H and D atoms were measured between 200 and 295 K in a laser-induced fluorescence-discharge flow-tube apparatus. The removal rates by H atoms were found to increase from 6.3 x 10 to the 13th power cu. cm/mol-sec at 295 K to 10 to the 14th power cu. cm/mol-sec at 200 K. The removal of HF(v = 3) by D atoms is somewhat slower, but the removal rates have a similar negative temperature dependence. There are several mechanisms by which H atoms can remove HF(v = 3), i.e., reaction to form H/sub 2/ + F or deactivation to HF(v = 0, 1, or 2) with or without exchange of the F atom. The several possibilities are discussed and compared to theoretical calculations.

High resolution absorption spectroscopy of NO2

Abstract The absorption cross-section of NO 2 has been measured above the 3979 predissociation limit in the region of 3920 and 3950 and in the discretely structured areas around 4112 and 4140 . Spectra were taken in a dual-beam arrangement using a tunable, pulsed dye laser with 0.05 bandwidth (FWHM). This represents an improvement of at least a factor of three over the resolution employed in previous studies. Below 3979 , the spectra are continous with occasional diffuse rotational lines superimposed. The spectra taken above 4100 reveal a wealth of structural complexity. We report here absolute cross-sections taken at 300 . The work above 4100 was also performed at 250 . Only slight variations in the measured cross-sections are observed between these two temperatures.

Behavior of singlet oxygen in the oxygeniodine transfer laser

The kinetic processes that affect the decay of (O2(1Δ) in the oxygeniodine transfer laser are discussed. The kinetics of O2* removal in the absence of iodine are now quite well established. A brief review of this topic is presented. When I2 is added to O2*, a distinction can be made between the behavior of O2* when both I2 and I are present, and when I2 is fully dissociated into atoms. In the latter case, energy pooling between O2(1Δ) and I* is the dominant process unless a strong I* quencher (e.g. H2O) is present. In the former case, the (O21Δ)-driven chain reaction mechanism for I2 dissociation is the dominant feature of the kinetics. A detailed description of each of these regimes is critical to the understanding of the oxygeniodine laser.

Vibrational relaxation of HF(v=1 and 3) in H2, N2, and D2 at 200 and 295 K

The vibrational relaxation rates of HF(v=1) and HF(v=3) have been measured in H2,N2, and D2 at 200 and 295 K. The v dependence of the relaxation rates is essentially the same for N2,D2, and several other diatomic molecules that deactivate HF via exothermic processes. The rates for HF(v=3) deactivation are larger than those for HF(v=1) by a factor of ∼18 at both 200 and 295 K.

Comment on ’’A paradox: The thermal rate coefficient for the H+DCl→HCl+D exchange reaction’’

Abstract : Experimental data are presented that show that chlorine atom abstraction from HCl by a colliding D or H atom is relatively slow at room temperature. These slow rates are much smaller than those obtained by trajectory calculations, suggesting that the activation energy for this process is > 3 kcal/mol. (Author)