ChemInform Abstract: STUDY OF THE REACTIONS MOLECULAR NITROGEN(1+) + 2(MOLECULAR NITROGEN) → TETRAATOMIC NITROGEN(1+) + MOLECULAR NITROGEN AND MOLECULAR OXYGEN(1+) + 2(MOLECULAR OXYGEN) → TETRAATOMIC OXYGEN(1+) + MOLECULAR OXYGEN FROM 20 TO 160 K BY THE C

The laws governing the dynamical behaviour of atoms and molecules are quantum mechanical, and specify that their internal energy states are discrete, with only definite photon energies inducing transitions between them, subject to selection rules. These energy levels appear as spectra in different regions of the electromagnetic spectrum: pure rotational lines in the microwave or far infrared, ‘rovibrational’ (rotation + vibration) lines in the middle and near infrared, while electronic transitions, sometimes with associated rotational and vibrational structure (‘rovibronic’) occur from the near infrared through the visible to the ultraviolet. An important feature of these spectra in the atmosphere is that they do not appear as single sharp lines, but are collisionally broadened about the central energy into ‘line shapes’ which frequently overlap with other transitions, both from the same molecule and from others. One of the primary dynamical quantities involved in the processes broadening these line shapes is the relative velocity of the molecules with which the photon absorbing and emitting molecules are colliding. These are primarily N2 and O2 in the atmosphere; if they have an overpopulation of fast moving molecules relative to a Maxwell–Boltzmann distribution, as we have suggested, the line shapes will be affected. Molecules such as carbon dioxide, water vapour, and ozone are all active in the infrared via rovibrational transitions, with water vapour being light enough and so having sufficiently rapid rotation that it has rotational bands appearing in the far infrared rather than the microwave. Nitrous oxide, N2O, and methane, CH4, are also active, but make smaller contributions because of their lower abundances. Molecular nitrogen and molecular oxygen, because they are homonuclear diatomic molecules, do not absorb or emit via electric dipole allowed transitions in the atmospherically important regions of the electromagnetic spectrum. Molecular oxygen, having a triplet ground state, does have weak forbidden and magnetic dipole transitions which, however, play only a very small role in the radiative balance. It should be noted that the translational energy of molecules in a large system like the atmosphere is effectively continuous rather than quantized.

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Temperature Intermittency and Ozone Photodissociation

Atmospheric Turbulence ◽

10.1093/oso/9780199236534.003.0008 ◽

2008 ◽

Author(s):

Adrian F. Tuck

Keyword(s):

Molecular Oxygen ◽

Molecular Nitrogen ◽

Prima Facie ◽

Rapid Quenching ◽

The Arctic ◽

Translational Energy ◽

Prima Facie Case ◽

Mixing Ratios ◽

Atmospheric Molecules ◽

Non Local

During the last two missions performed by the ER-2 in the Arctic lower stratosphere, POLARIS in the summer of 1997 and SOLVE during the winter of 1999–2000, an unexpected correlation emerged when the data were subjected to analysis by generalized scale invariance. It was between the intermittency of temperature, a number which can be determined for each segment of analysable flight from the temperature measurements, and the average over the flight segment of the photodissociation rate of ozone, which was calculable as a time series along the flight segment by taking the product of the 1Hz measurements of the local ozone concentration and the 1Hz measurements of the ozone photodissociation coefficient. In searching for a physical explanation of this correlation, it was realized that the common link between the quantities was that ozone photodissociation produces photofragments of atomic and molecular oxygen that recoil very fast, while temperature itself is the integral of the translational energy of all air molecules. The next step therefore was to ask if the intermittency of temperature was correlated with the average of the temperature itself over the flight segment: it was. One might think that because ozone is present at about 20km altitude in mixing ratios of about 2−3×10−6, the rapid quenching of the translational energies of the recoiling photofragments by molecular nitrogen and molecular oxygen would prevent any possible effects from showing up in the bulk, observed temperature. However, during the POLARIS mission, it was possible to fly the ER-2 near the terminator, the boundary between day and night, because at Arctic latitudes the planet was rotating slowly enough that it could fly legs in the same, stagnant air mass in both sunlight and darkness. These flights showed that the heating rate was significant, about 0.2Kper hour, and since heating in the stratosphere arises from the absorption of solar radiation by ozone, which leads to photodissociation, there is a prima facie case for considering non-local thermodynamic equilibrium effects from the recoiling fast photofragments. Two arguments may be deployed at this point, both from the theoretical literature; there are as yet no experiments on the translational speed distributions of atmospheric molecules.

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