David L. McFadden

Rate constants for the reactions of atomic boron with O2, SO2, CO2, and N2O

The gas phase reactions of atomic boron with O2, SO2, CO2, and N2O have been studied using a diffusion flame technique. Atomic boron is produced in a microwave discharge of 1% B2H6 in helium and diffuses into a chamber containing the oxidizer also diluted in helium. The temperature was approximately 300 °K. The rate constants were determined from atomic absorption measurements of boron density in the flame. The rate constants for the O2 and SO2 reactions are (9±7) ×10−12 cm3 molecule−1sec−1 and (7±5) ×10−12 cm3 molecule−1sec−1, respectively. An upper limit of 5×10−13 cm3 molecule−1sec−1 is estimated for the rate constants of the CO2 and N2O reactions.

Chemiluminescence from the gas phase reaction of atomic boron with the alkali metal fluorides

Gas phase reactions of boron with CsF, RbF, KF, and NaF were studied in a merged flow. Atomic boron was produced in a microwave discharge of a B2H6–helium mixture. The densities of ground state boron and alkali atoms produced in the reaction were determined by absorption measurements. Light from excited alkali atoms in the reaction region was recorded and the excited state population densities were calculated. Our evidence indicates that alkali atoms (M) in the first excited P states are produced primarily in the direct reaction B+MF→BF+M. Several additional processes contribute to the production of higher excited states. Population inversion is observed between a number of excited states.

Temperature dependence of rate coefficients for thermal electron attachment reactions of CH3Br, CF3Br, and CF3I

Abstract Rate coefficients for electron attachment reactions of CH 3 Br, CF 3 Br and CF 3 I have been measured as a function of temperature. Absolute rate coefficients were obtained at 293 K for SF 6 , CH 3 Br, CF 3 Br and CF 3 I; in units of cm 3 molecule −1 s −1 the values are 2.2 × 10 −7 for SF 6 ; 6.3 × 10 −12 for CH 3 Br; 1.2 × 10 −8 for CF 3 Br; and 2.2 × 10 −7 for CF 3 I. Rate coefficients are reported for CH 3 Br, CF 3 Br and CF 3 I at 293, 615, and 777 K from relative rate measurements by using SF 6 as a reference compound. Mass spectral analysis of product negative ions confirmed a dissociative attachment mechanism.

Electron attachment reactions of perfluoroalkyl transition metal carbonyls: Rate constants and product analysis

Absolute rate constants for electron attachment reactions of CF3Mn(CO)5, CF3Co(CO)4, and C2F5Co(CO)4 have been measured in a gas flow system with electron cyclotron resonance (ECR) detection. Free electrons were generated by Penning ionization of argon gas by helium metastables produced in a low power radio‐frequency discharge. The pressure was 2.3–2.5 Torr. The rate constants at 293 K in units of cm3 molecule−1 s−1 are (3.5±0.6)×10−7 for CF3Mn(CO)5; (2.0±0.4)×10−7 for CF3Co(CO)4; and (1.8±0.3)×10−7 for C2F5Co(CO)4. Negative ion mass spectra indicate that nondissociative attachment is important at thermal electron energy. The cross section for nondissociative capture falls rapidly with increasing electron energy. Dissociative product channels are also observed. Electron capture rate constants for several additional molecules are presented and compared with values from the literature. The rate constants in units of cm3 molecule−1 s−1 are 2.8×10−7 for SF6; 3.7×10−7 for CCl4; 3.1×10−7 for CFCl3; 1.8×10−9 for...

Observation of the optoacoustic effect in the microwave region

The microwave analog of the optoacoustic effect has been observed. Collisional relaxation of absorbed microwave energy between Zeeman magnetic sublevels of gaseous molecular oxygen results in the production of an acoustical signal which is detected by a sensitive microphone.

Gas-phase atom—radical kinetics of N and O atom reactions with CF and CF 2 radicals

Abstract Rate constants for the reactions of N and O with CF and CF 2 radicals have been measured in a gas-flow system with photoionization mass spectrometry detection. CF( X 2 Π 1 2 3 2 ) and CF 2 ( X 1 A 1 ) radicals were produced in a radiofrequency discharge of CFBr 3 and CF 2 Br 2 , respectively. Atomic reactants were produced from the corresponding elemental gases in a microwave discharge. The pressure was 1.7 Torr. The rate constants for fluorocarbon radical decay under pseudo-first-order conditions at 293 K in units of cm 3 molecule −1 s −1 are (3.4 ± 0.5) × 10 −12 for CF+N; (7.2 ± 1.0) × 10 −12 for CF 2 + N; (1.2 ± 0.2) × 10 −11 for CF+O; and (2.0 ± 0.4) × 10 −11 for CF 2 +O.

Efficient vibrational excitation of gaseous CF4 and C2F6 by low-energy electrons

Abstract Evidence is presented from a linewidth study of electron cyclotron resonance (ECR) absorption for efficient T → V energy transfer between low-energy electrons ( 4 and C 2 F 6 . It is suggested that this excitation proceeds by means of a direct mechanism.

Noise reduction in EPR discharge‐flow studies

In discharge-flow systems employing electron paramagnetic resonance detection, intense spectrometer noise is present under certain conditions. This noise is due to free electrons produced in the discharge and can be eliminated by the addition of an electron scavenger to the flow. Using SF6 to suppress the noise, EPR spectroscopy can be used to identify and study transient species within a millisecond after their formation in an electrical discharge.

Chemiluminescence from the gas phase reaction of atomic carbon with lead oxide

Abstract The gas phase reaction C + PbO → CO + Pb was studied. The relative population distribution of the electronically excited Pb produced in this reaction was determined. The total cross section for the reaction and the cross section for the production of electronically excited states are estimated to be 20 and 5 A 2 respectively.

Detection of several electronically metastable atomic states by gas phase EPR

Abstract Several atomic metastable species including N(2D 5 2 ), N(2D 3 2 ), N(2P 3 2 ), O(1D2), Ne(3P2), Ar(3P2), Kr(3P2 and Xe(3P2) have been detected by gas phase electron paramagnetic resonance (EPR) in a discharge-flow system. Spectra and absolute concentration are presented.