Herzberg continuum

FIGURE 4-1 Potential energy curves for ground and first four excited states of 02. S-R = Schumann-Runge system, H = Herzberg continuum, A-A = atmospheric bands (adapted from Gay-don, 1968). 

Yoshino, K., J. R. Esmond, A. S.-C. Cheung, D. E. Freeman, and W. H. Parkinson, High Resolution Absorption Cross Sections in the Transmission Window Region of the Schumann-Runge Bands and Herzberg Continuum of 02, Planet. Space Sci.., 40, 185-192... 

Collision-induced absorption of gaseous oxygen in the Herzberg continuum, p. 183, 2003. In Ref. [10]. 

Herzberg Continuum (adiabatic curve following two 0(3P2) atoms)... 

From 200 to 242 nm, the 02 absorption, which is related to the Herzberg continuum with low absorption cross section, occurs in the stratosphere. In this spectral region, the ozone absorption must be introduced since the 03 Hartley band is characterized by high values of the absorption cross section between 200 and 300 nm. The simultaneous absorption by 02 and 03 must be considered in the stratosphere, whereas the O3 absorption is practically negligible in the mesosphere since the total number of absorbing ozone molecules is small. 

Several laboratory measurements of the total absorption cross-section for the critical 02(A S u - X 2 g) Herzberg continuum have been reported... 

Fig. 2. Cross section for oxygen absorption in the Herzberg continuum region above 200 nm. [Sources ( ) Ditchburn and Young, 1962, ( ) Shardanand, 1969, (A) Ogawa, 1971, (V) Hasson and Nicholls, 1971, ( ) Shardanand and Rao, 1977].

Measurements of the concentration of OH radicals in the stratosphere in the altitude range 34—37 km have been made by balloon-borne LIDAR. The first post-sunset concentration levels were reported and comparisons were made with current 1-dimensional models. The effects of reduced absorption cross-sections for O2 in the Herzberg continuum on the composition of the stratosphere have been examined by Brasseur et ai., " following the suggestion that laboratory values for the cross-sections might be overestimated by as much as 30—50%. A model for the circulation of atmospheric CO has been described by Pinto et and which includes photochemical production and... 

Figure 4-31. Absorption cross section of molecular oxygen in the Herzberg continuum between 194 and 240 nm (From Yoshino et al, 1988).

As shown by Johnston and Selwyn (1975), the cross section of N2O varies strongly with temperature. The quantum yield for photodissociation is unity, and the products are N2 and 0(1D). The atmospheric photolysis rate comes predominantly from the absorption of solar radiation in the 02 Herzberg continuum and Schumann Runge bands. Jn2o 9 x 10-7s-1 for A > 175 nm. 

The absorption cross sections (Figure 4.50) for hydrochloric acid (or hydrogen chloride) HC1 were measured by Vodar (1948), Romand and Vodar (1948), and Romand (1949), and later by Inn (1975). The latter measurements extend from 140 to 220 nm, leading to a photodissociation frequency of about 3 x 10-6s-1 at zero optical depth. To calculate Jhci in the atmosphere, the Schumann Runge bands and continuum must be considered, as well as the Herzberg continuum. 

Brasseur, G., A. De Rudder, and PC. Simon, Implication for stratospheric composition of a reduced absorption cross section in the Herzberg continuum of molecular oxygen. Geophys Res Lett 10, 20, 1983. 

Cheung, A.S.-C., K. Yoshino, W.H. Parkinson, S.L. Guberman, and D.E. Freeman, Absorption cross section measurements of oxygen in the wavelength region 195-241 nm of the Herzberg continuum. Planet Space Sci 34, 1007, 1986. 

Frederick, J.E., and J.E. Mentall, Solar irradiance in the stratosphere Implication for the Herzberg continuum absorption of O2. Geophys Res Lett 9, 461, 1982. 

Froidevaux, L., and Y.L. Yung, Radiation and chemistry in the stratosphere Sensitivity to O2 cross sections in the Herzberg continuum. Geophys Res Lett 9, 854, 1982. 

Jenouvrier, A., B. Coquart, and M.F. Merienne-Lafore, New measurements of the absorption cross sections in the Herzberg continuum of molecular oxygen in the region between 205 and 240 nm. Planet Space Sci 34, 253, 1986. 

Shardanand and A. D. P. Rao (1977). Collision-induced absorption of 02 in the Herzberg continuum. J. Quant. Spoctrosc. Radiat. Transfer 17, 433-439. 

Figure 4.14 shows the photodissociation rate coefficient for 02, namely, j0l, as a function of altitude above 30 km. From 30 to 60 km, the Herzberg continuum provides the dominant contribution to j0l At about 60 km, the contribution from the Schumann-Runge bands equals that from the Herzberg continuum above 60 km, the Schumann-Runge bands predominate until about 80 km, where the Schumann-Runge continuum takes over. In the mid-to upper stratosphere, at solar zenith angle = 0°, an approximate value of jo2 is jo2 — 10 9 s. ... 

Although the absorption cross section of oxygen at 193 nm is relatively small cm ), since it comprises 21% of air, its overall effect in the attenuation of photons and the production of reactive excited-state species is quite significant. Its contribution to absorption shows a marked increase from 200 nm to 180 nm and a marked decrease from 200 nm to 250 nm in the Herzberg continuum, where the ozone absorption becomes significant. 

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