Schumann-Runge

Cheung A S C, Yoshino K, Freeman D E, Friedman R S, Dalgarno A and Parkinson W H 1989 The Schumann-Runge absorption-bands of 0 0 in the wavelength region 175-205 nm and spectroscopic constants of isotopic oxygen molecules J. Mol. Speotroso. 134 362-89... 

Ackermann M and Biaume F 1970 Structure of the Schumann-Runge bands from the 0-0 to the 13-0 band J. Mol. Spectrosc. 35 73-82... 

High-temperature sulfur vapor at low pressure is said to be pale-violet due to the presence of S2 [22]. The S2 molecule in its triplet ground state has also been produced by photolysis of H2S2 [23], S2CI2 [20, 24], and Me2S2 [25], for example. The S2 vapor spectrum is characterized by the Schumann-Runge bands transition Voo=316 nm [26]) which at high temper-... 

The setup used for crossed beam experiments is basically the same apparatus used in the H2O photodissociation studies but slightly modified. In the crossed beam study of the 0(1D) + H2 — OH + H reaction and the H + HD(D2) — H2(HD) + D reaction, two parallel molecular beams (H2 and O2) were generated with similar pulsed valves. The 0(1D) atom beam was produced by the 157 photodissociation of the O2 molecule through the Schumann-Runge band. The 0(1D) beam was then crossed at 90° with the... 

The X3 -—> B3X- transition is allowed and as seen in Figs. 4.2 and 4.3 results in an absorption in the 130-to 200-nrn region known as the Schumann-Runge system. The banded structure from about 175 to 200 nm corresponds to transitions from v" = 0 as well as v" = 1 (i.e., hot bands) of the ground X3S state to different vibrational levels of the upper state. 

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). 

FIGURE 4.2 Absorption coefficients for 02 in the Schumann-Runge continuum. Note log scale. (Adapted from Inn, 1955.)... 

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... 

B. Atomspheric photochemistry. The photodissociation of oxygen in sunlight is the major photochemical process occurring in earth s atmosphere. The first intense allowed transition in O., is B - X 32 which occurs at 202.6 nm and is called the Schumann-Runge band system (Section 2.8). It merges intoa continuum beyond 175.9 nm and correlates with one oxygen atom 0(23P) in the ground state and one in the excited state O (2 D)... 

The onset of the continuum of the Schumann-Runge absorption bands of 02 is at 1750.5 A. The lower electronic state of the transition is the ground state and dissociates to ground-state oxygen atoms the excited... 

Fig. V-12. Absorption coefficients of O, in the region 1100 to 2000 A. k is in units of atm em 0°C, base e. 1300 to 1700 A, Schumann-Runge continuum. 1750 to 1950 A, Schumann-Runge bands. From Watanabe c al. (1014), reprinted by permission. Copyright 1953 by the American Institute of Physics.

Fig. V-13. The absorption cross sections of the 02 continuum in the 1814 to 2350 A region, a is in units of 10"22 cm2 molec base e, at room temperature. The absorption cross sections are measured at minima between the well-separated rotational lines of the Schumann-Runge bands for X < 2025 A. a increases with pressure probably as a result of the formation of 04. The data are values at the low pressure limit. From Ogawa (755), reprinted by permission. Copyright 1971 by the American Institude of Physics.

The Schumann-Runge bands converge to the limit at 1750 A corresponding to the production of Of3/3) + Of1/)). The integrated absorption coefficients of the Schumann-Runge system from (0,0) to (20,0) have been... 

Fig. V-14. Potential energy curves of Oj. S-R, Schumann-Runge bands H, Herzberg bands A-A, atmospheric bands. The line-broadening was observed at r = 4 of the fl3 state at which point the repulsive 3n. state crosses the B5I state. See Murrell and Taylor (726). From Dissociation Energies and the Spectra of Diatomic Molecules" by Caydon, 3rd Ed. 1968, p. 74, reprinted by permission of Associated Book Publishers Ltd.

Ackerman and Biaume (37) have observed that rotational lines become diffuse at if = 4, 8, and 11 for the Schumann-Runge system. They attribute the difluseness to predissociation. 

Plwtodissociatiqn of 02 in the Upper Atmosphere. The source of O atoms above an altitude of 50 km is mainly from the photolysis of 02 in the Herzberg I and Schumann-Runge continua (488). The predissociation of 02 in the Schumann Runge bands (r > 3) [Wray and Fried (1054)] is the additional source of O atoms between 65 and 95 km. Supporting evidence of the predissoeiation is that no fluorescence of the Schumann-Runge bands above v > 1 has been observed in the upper atmosphere. 

A small amount of 0( >) is produced from the r" = 1 and 2 levels by absorption of the solar radiation below 1850 A of the Schumann-Runge continuum (40) contributing to Of1D) atoms in the mesosphere and stratosphere. 

O2(h X + ) in the Upper Atmosphere. The atmospheric band of O, observed in the upper atmosphere (40 to 130 km) indicates that the 02( ) is produced by photochemical processes (1000). The most likely process is the photolysis of 02 in the Schumann-Runge continuum followed by the energy transfer reaction (350)... 

Schumann-Runge Continuum (adiabatic curve following one 0(3P2) atom, one O( D) atom)... 

Another important spectral range, between 200 and 175 nm, is related to the 02 Schumann-Runge band system which includes 18 bands, (2-0) to (19-0) subject to the predissociation processes, particularly in the mesosphere. 

Fig. 2. Absorption spectrum of oxygen in the Schumann-Runge band system. The absorption coefficient, k, is defined by the equation I = la exp ( — kx), where h and I are the incident and transmitted light intensities and x is the layer thickness of the absorbing gas reduced to STP. This figure is taken from ref. (101) with the permission of The Journal of Chemical Physics.

The most recent measurements of the absorption coefficients of oxygen have been made by Watanabe et al. (101). For the transition 32u- -32 absorption intensities in the Schumann-Runge bands are shown in Figure 2 and in the Schumann-Runge continuum in Figure 3. 

Fig. 3. Absorption spectrum of oxygen in the Schumann-Runge continuum. This figure is taken from ref. (101) with the permission of The Journal of Chemical Physics.

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