Laboratory CO2 photolysis studies related to planetary atmospheres

The CO(a 3II) state, the upper state of the Cameron bands, was characterized with respect to its average radiative lifetime and its quenching coefficients for a series of simple molecules. The CO2 recombination reaction (O(3P) + CO + M yields CO2 + M) was studied as a function of temperature. For M = CO, the rate constant can be expressed as k = 6.5 x 10/33 exp(-4340 plus or minus 550/RT) cm to the 6th power molec/2 sec/1, whereas the rate for M = CO2, the pertinent species in the planetary atmospheres, is 1.6 times greater. The quantum yield for CO2 photodissociation was measured in the 1200-1500 A region, using atomic line sources. The yield throughout this spectral region was much lower than that measured at 1470 A, the lowest value obtained being 8% at 1304 A

Photodissociation of CO2 and quenching of metastables

Investigations in four different areas were carried out to further our understanding of the chemistry of the atmospheres of Mars and Venus. CO2 photodissociation quantum yields were determined in the 1300-1500 A spectral region by measuring both CO and oxygen atoms. The O(1S) quantum yield was determined for CO2 photodissociation in the 1060-1175 A spectral region. The measurement resolves the differences between two earlier experiments, and demonstrates that the O(1S) yield is unity throughout most of the measured region. The pathways for the quenching of O(1S) by N2O, CO2, H2O and NO were investigated and the source of the Venus nightglow, detected by Venera 9 and 10, was investigated. What appears to be a new O2 band system, was detected although the identity of the transition is not yet evident

The source of stratospheric NO and N2O

The photodissociation of O3 was investigated as a possible sources of N2O production in the stratosphere. Photolysis was conducted at 1576 A to generate the excited O2 states that react with N2 to form N2O. At this wavelength, there is a quantum yield of two for prompt production of oygen atoms, which is a consequence of the existence of two photodissociative channels giving comparable yields. One of these channels gives O(D1) and O2(b1sigma(+)subg), with a quantum yield of 0.6, whereas the other results in fragmentation of the O3, with production of three ground state oxygen atoms. The O2(b) is generated with vibrational excitation, and there are comparable populations in levels O to 3. These observations are the first to show O2(b) production from any photodissociative process, and were made under conditions in which the kinetics of vibrationally excited O2(b) can be studied. It appears that O3 photodissociation at 1576 A is not a good system for generating the higher electronic states of O2; it is likely that better results will be obtained at 1930 A

Laboratory CO2 photolysis studies related to planetary atmospheres Semiannual report, 15 Jul. 1969 - 15 Jan. 1970

Oxygen and carbon dioxide UV photolysis studied with resonance fluorescence to analyze planetary atmospheric processe

Laboratory CO2 photolysis studies related to planetary atmospheres Final report, 15 Jul. 1969 - 15 Jul. 1970

Photolysis of CO-2 in UV spectral region applied to models of Martian and Venusian atmosphere

CO2 photodissociation and vibrational excitation in the planetary atmospheres

The principal subjects of investigation were the determination of the CO2 photodissociation quantum yields at the wavelengths from 1200 A to 1500 A, and the efficiency of electronic-to-vibrational energy transfer in the systems 0(1D) + CO, N2, CO2 yields 0(3P) + CO N2, CO2 vibrational energies. Measurements on the photodissociation quantum yield of CO2 in the 1200-1500 A region show that it is wavelength dependent, and for the six atomic line sources used, the quantum yield varied from 0.2 to 0.8. The data appear to fit the interpretation of stable CO2 bound states mixed with repulsive or predissociating states, since the low quantum yields coincide with the maximum structure in the CO2 absorption spectrum. The first reliable measurements were made on the efficiency of electronic-to-vibrational energy transfer in the systems 0(1D)-CO and 0(1D)-N2, using a uv resonance fluorescence technique. The 0(1D)-CO2 interaction was investigated by infrared techniques

O₂ photoabsorption in the 40 950–41 300 cm⁻¹ region: New Herzberg bands, new absorption lines, and improved spectroscopic data

The technique of cavity ring‐down (CRD) spectroscopy is particularly useful for measuring absorptions of very weak optical transitions. We have in this manner investigated the 40 950–41 300 cm−1 region in O2, where only absorption in the O2(A 3Σ+u–X 3Σ−g) 11‐0 band had been previously identified. Five new bands have been discovered in this range—the A′ 3Δu–X 3Σ−g 12‐0 and 13‐0 bands, the c 1Σ−u–X 3Σ−g 17‐0 and 18‐0 bands, and the A 3Σ+u−X 3Σ−g 12‐0 band. The origins of the F1 and F2 components of the latter lie only 7 cm−1 below the lowest dissociation limit, and 15 lines have been identified. No F3 levels were observed; apparently all are above the dissociation limit. The high instrumental sensitivity of the CRD technique has allowed observation of weak lines of the A–X 11‐0 band, and 12 of the 13 branches have been identified and their intensities measured. A very low upper limit has been set on the intensity of the thirteenth branch, Q13. We find 107 unidentified lines in the region, the stronger ones (19) lying in the vicinity of lines of the A–X 11‐0 band. The weaker ones (88) are spread throughout the spectral region, up to and even beyond the O2dissociation limit, and probably have their origin in transitions to very weakly bound O2 states, which may have atmospheric significance. These weaker lines have intensities that are typically 1%–5% of the strong A–X 11‐0 band lines

Studying Atomic Physics Using the Nighttime Atmosphere as a Laboratory

A summary of our recent work using terrestrial nightglow spectra, obtained from astronomical instrumentation, to directly measure, or evaluate theoretical values for fundamental parameters of astrophysically important atomic lines