K. H. Welge

Collisional Deactivation of O(1S)

Absolute rate coefficients for the collisional deactivation of O(1S) have been measured for CO2, CO, SF6, O2, H2O, NH3, CH4, C2H4, C2H6N2O, NO, NO2, H2, N2, He, Ne, Ar, Kr, and Xe. The measurements have been made with a lifetime technique in which O(1S) is produced in the photodissociation of CO2 by a pulsed vacuum‐ultraviolet light source The rate coefficients were obtained from time‐resolved measurements of the intensity of the O(1S → 1D) line at 5577 A. Deactivation of O(1S) by collision induced radiation has been observed for H2, N2, Ar, Kr, and Xe.

Temperature Dependence of O(1S) Deactivation by CO2, O2, N2, and Ar

The collisional deactivation of O(1S) by CO2, O2, N2, and Ar has been investigated as a function of temperature in the range from 200 to 450°K. O(1S) was produced in a pulsed mode by vacuum ultraviolet flash photolysis of CO2. The decay of O(1S) was observed by the 5577 A emission as a function of time after the production pulse. Deactivation rate constants were derived from the dependence of the decay rate on the concentrations of added gases. Arrhenius plots yielded the following results: kCO2=3.3× 10−11 exp(−2630± 200/RT) cm3molecule−1· sec−1,kO2=4.9× 10−12 exp(−1700± 200/RT) cm3molecule−1· sec−1,kN2<5× 10−17cm3molecule−1· sec−1 (independentoftemperature),kAr<5× 10−17cm3molecule−1· sec−1 (independentoftemperature). In the case of N2 and Ar the collisional enhancement effect of the O(1S) emission was observed and was found to be independent of temperature.

Photodissociation of O3 in the Hartley Band. Reactions of O(1D) and O2(1Σg+) with O3 and O2

The ultraviolet photolysis of O3 in the presence and in the absence of O2 has been investigated in the wavelength region ∼ 2375–2625 A using flash photolysis and kinetic emission spectroscopy with a time resolution high enough to allow unambiguous identification of photodissociation products. The production of O(1D) was established by observing the forbidden 1D → 3P emission at 6300 A. The decay of the emission provided a value of the rate constant for the O(1D)–O3 reaction of (2.5 ± 1) × 10−10 cm3 molecule−1·sec−1 at 25°C. Analysis of the O(1D) decay showed that the rate of chain reactions in which O(1D) could be reproduced must be smaller than the O(1D)–O3 quenching rate by more than an order of magnitude. No emission was observed from O2(1Σg+) when O3 alone was photolyzed, indicating that the primary yield for O2(1Σg+) production is smaller than 1/20 of the O(1D) production. O(1D) was very efficiently quenched when N2 and O2 were added. O2(1Σg+) was observed by the 1Σg+ → 3Σg− emission when O3–O2 mixtu...

Erratum: Flash Photolytic Production, Reactive Lifetime, and Collisional Quenching of O2(b 1Σg+, v′=0)

Collisional quenching of O2(b 1Σg+, υ′ = 0) at room temperature by O2 and a variety of foreign gases has been investigated with a pulsed lifetime measurement technique. O2(b 1Σg+, υ′ = 0) has been produced in a pulsed mode through flash photolysis of O2 in the vacuum uv and has been detected through the emission of the (0, 0) band at 7620 A of the forbidden O2(b 1Σg+ → X 3Σg− transition. The (0, 0) band intensity has been measured as a function of time after the photolysis flash and as a function of the O2 and foreign gas pressures. Quenching rate constants are derived from the reactive lifetimes. The photolytic production of O2(b 1Σg+, υ′ = 0) from O2 and the quenching by O2 has been studied at O2 pressures from 0.02–100 torr. The observations at low O2 pressures from 0.02 to about 1 torr are consistent with the previously established fast O2(b 1Σg+) production mechanism, O2 + hν → O(1D) + O(3P), O(1D) + O2(X 3Σg−) → O(3P) + O2(b 1Σg+), in the Schumann–Runge continuum region. No emission of the (1, 1) an...

Absolute Rate Constant for the Reaction H+H2CO

The photolysis of formaldehyde in the pronounced absorption region ∼1700–1760 A has been investigated. The production of H atoms has been established by direct observation using pulsed photolysis and time dependent observation of the Lyman‐α resonance fluorescence at 1216 A. From the measurement of the H‐atom decay under pseudo‐first order conditions the rate constant for the reaction H+H2CO→ H2+HCO has been obtained. The result is 5.4± 0.5× 10−14 cm3 molecule−1· sec−1 at 297°K.

Rotation‐Vibration Energy Transfer in Collisions between OH(A 2Σ+) and Ar and N2

Collisional relaxation of OH(A 2Σ+, υ′, K′) in high rotational levels of υ′ = 0 and 1 has been investigated with respect to transitions from rotational levels in υ′ = 0 to levels in υ′ = 1. Initial nonequilibrium rotational distributions of OH(A 2Σ+) in υ′ = 0 and 1 were produced by monochromatic photodissociation of H2O with the radiation of a krypton resonance lamp at 1236 and 1165 A. The effect of added foreign gases (Ar and N2) on the population of individual levels in υ′ = 0 and 1 has been studied under steady‐state conditions by observing the emission intensities of individual lines in the (0, 0) and (1, 1) bands of the OH(A 2Σ+→X 2Π) transition. The essential observation was made on the population of the rotational level K′ = 15 in υ′ = 1. The population of this level increased significantly in the presence of Ar and N2 beyond the initial population produced from H2O alone. In comparison, the population of adjacent levels remained relatively unchanged or decreased when foreign gas was added. The ef...

Collisional quenching of O(1S) by rare gas atoms and collision‐induced emission by O(1S)‐rare gas eximers

The quenching and collision‐induced emission of the O(1S) atom by the rare gas atoms M=Xe, Kr, Ar, Ne, He has been investigated at 201 and 291 K. After pulsed photolytic production of O(1S) the emission decay rate as well as the intensity was investigated as a function of added gas concentration. Second‐order O(1S) collisional quenching coefficients, kexp, and efficiency coefficients, k*exp, for the collisionally induced eximer emission have been measured. The formation of the O(1S)Xe eximer occurred with thermal equilibrium in the O(1S)Xe state by steady‐state termolecular recombination, the O(1S)Xe potential well depth being ∼0.06 eV. For Kr, Ar, Ne,and He the quenching and emission enhancement did not exhibit a temperature dependence, showing that thermal equilibrium and steady‐state recombination was applicable. The potential depths are small compared to kT, where T=201 K. The O(1S) removal occurs practically only via O(1S) + M (+ M ) ⇄krkf O(1S)M(+M), O(1S) M→A*O(1S)M+hv, with A* being an averaged mo...

Photodissociative production of O(1S) from CO2, O2, O3, and N2O at the 1216‐Å Lyman‐α line

The production of O(1S) in the photodissociation of CO2, O2, O3, and N2O has been investigated at the 1216‐A Lyman‐α line. Relative quantum yields at this wavelength have been determined: φN2O: φCO2:φO2: φO3=1.0:(0.31 ± 0.06):(0.03 ± 0.01):<0.03. These must be upper limits for the absolute quantum yields.

Relative efficiencies of O(1S) production from photodissociation of Co2 between 1080 and 1160 Å

Relative O(1S) emission intensities following the phtotdissociation of CO2 have been measured between 1080 and 1160 A as a function of incident photon energy at 2–3 A wavelength intervals with 3.2 A bandpass. Most of the structure in the absorption spectrum of CO2 was clearly folowed by the O(1S) intensities in the range 1098–1160 A, whereas the structure was not followed below 1098 A. Relative quantum efficiencies for the photodissociative production of O(1S) from CO2 were highest in the range 1095–1135 A and dropped on both sides of this range.

Time‐of‐Flight Spectroscopy of Metastable Photodissociation Fragments. N2O Dissociation in the Vacuum uv

The photodissociation of N2O involving electronically excited metastable fragments has been investigated at wavelengths ≳ 1050 A by photofragment translational energy spectroscopy. Irradiation was carried out with light pulses of a few microseconds duration, and fragment energies were measured by means of the time‐of‐flight technique. Auger electron emission from metal surfaces, cesium and brass, was used to detect metastable fragments after a flight path length of 46 cm. Experiments have been made in the wavelength regions ∼ 1050–1440, ∼ 1250–1440, and ∼ 1350–1440 A. Formation of the metastables N2(A 3Σu+) and O(1S) in the processes N2O→N2(A 3Σu+)+O(3P) and N2O→N2(X 1Σg+)+O(1S) has been observed. O(1S) appeared in a translational energy range from ∼ 3 to 1 eV, and N2(A 3Σu+) in a range from ∼ 1 to 0.1 eV. O(1S) produced electron emission upon deactivation at a cesium‐cated surface, and N2(A 3Σu+) produced electron emission upon deactivation at a cesium and also a bare brass surface.