Atmospheric absorption of near infrared and visible solar radiation by the hydrogen bonded water dimer

Abstract

Based on the physico-chemical properties of water dimers, their near infrared and visible absorption of solar radiation in the earth's atmosphere is calculated. The calculation uses equilibrium constants determined by statistical mechanics, and a vibrational absorption spectrum determined by a coupled oscillator quantum mechanics model and ab inirio quantum chemistry. The resulting total atmospheric absorption was calculated using a line-by-line radiative-transfer model, and depends significantly on the dimer abundance, as well as on the frequency and line width given to vibrational transitions. The best estimate achieved for the possible range of total absorption from 400 nm to 5000 nm by water dimer in the tropics is 1.63.3 W m-2. In a global-warming scenario, the increased temperature and water vapour partial pressure result in a nonlinear increase in the absorption of solar radiation by water clusters. Most of the energy from water dimer absorption is deposited in the lower troposphere, particularly in the tropics, tending to make it more convective.

Infrared shifts of the water dimer from the fully flexible ab initio HBB2 potential

“…0.00(0.75) / 0.00(0.69) (2) 11.18(0.65) / 10.16(0.61) (2) 11.66(0.54) / 11.53(0.50) new HBB/PS potential, which incorporates the empirically adjusted PartridgeSchwenke [51] monomer potential, was not available. However, the IR shifts that we define with respect to the calculated isolated monomer frequencies are expected not to depend too much on these discrepancies.…”

Perspective: Water cluster mediated atmospheric chemistry

“…To evaluate the role of water complexes, their abundance has to be determined as a function of altitude. [8][9][10][11][12][13] In principle, atmospheric abundance of complexes can be obtained from the temperature dependent equilibrium constant K eq (T) and the partial pressure of constituent monomers. For such estimates it is necessary to obtain the binding energy and the vibrational and rotational partition functions for the complex and its constituent monomers.…”

“…5-7, 10, 22, 43, 44 Water complexes can be diffuse absorbers of solar radiation, contributing to atmospheric heating, an effect resulting from changes occurring upon complex formation in the IR and near IR spectra of constituent monomers. 7,8,[10][11][12]45 Intermolecular interactions responsible for complex formation cause shifts and increased linewidth in ro-vibrational spectra of water complexes compared with the constituent monomers, thereby enhancing their "greenhouse" gas potential. 8,11 Only water complexes with abundant atmospheric gases have atmospheric concentrations large enough to affect radiative transfer.…”

The H<sub>2</sub>O-O<sub>2</sub> water vapour complex in the Earth's atmosphere

“…Among the bound complexes, water vapour complexes (H 2 O-X with, e.g., X = H 2 O, O 2 or N 2 ), are expected to have a combined surface abundance at the ppmv level, as estimated by statistical thermodynamic calculations (for example, Vaida et al, 2001). This represents ten times the amount of CO or N 2 O and would place hydrated complexes among the ten most abundant molecular compounds at ground level.…”

“…In the past 2-3 decades, numerous laboratory and theoretical studies of bound complexes have been published (e.g., Tao et al, 1996;Paul et al, 1997;Svishchev and Boyd, 1998;Vaida et al, 2001;Headrick and Vaida, 2001;Robinson and Kjaergaard, 2003;Paynter et al, 2009). …”