3 Solar flux at Earth’s surface VisibleNIRIRO3Electronic transitionsO2H2O, v=3Vibrational transitionsH2OH2O, v=2H2OCalculated clear sky direct solar flux at Earth’s surface from known absorbers in the atmosphere.
4 Complexes in the Atmosphere O2•O2 and O2•N2 complexes have been shown to absorb about 1 W/m2 of incoming solar radiation.Solomon, Portmann, Sanders, Daniel, JGR 1998.Hydrated complexes, H2O•X, are likely to contribute.H2O•H2OH2O•O2H2O•N2Contribution depends on position, intensity and shape of spectroscopic transitions as well as atmospheric abundance.Nature, 1969.Vaida, Daniel, Kjaergaard, Goss, Tuck, QJRMS 2001.
5 Water dimer, H2O•H2O CCSD(T)/aug-cc-pV5Z optimized geometry H donor CCSD(T)/CBSROO = Å0.965Å0.958Å+anharm corrROO = 2.97Å0.960ÅWater monomer,ROH = 0.959ÅExpt. (Dyke)ROO = 2.976ÅH donorH acceptorOH bond involved in hydrogen bonding is significantly longer frequency red shiftLane, Kjaergaard, JCP 2009.
6 Water dimer, H2O•H2O Simple vibrational model for water dimer Each H2O unit is modeled by two OH-stretching and one HOH-bending local mode oscillator.We use the Harmonically Coupled Anharmonic Oscillators (HCAO) local mode model for each of the H2O units.Determine local mode parameters and dipole moment functions from ab initio calculations.Low, Kjaergaard, JCP 1999.Schofield, Kjaergaard, PCCP 2003.
7 HCAO model for donor unit Dipole moment function
8 Stretch fundamental region Long path length 351K with water monomer abs subtracted.Paynter, Ptashnik, Shine, Smith, GRL 2007Schofield, Kjaergaard, PCCP 2003
9 Band frequencies (cm-1) Water dimer, far-IRMatrix isolation experiment versus anharmonic calculationModeBand frequencies (cm-1)Ne-matrixp-H2-matrixVPT2 (calc)7522.44854958309.1299.13049173145.914410151121.212211122.21211275.785Ceponkus et al, JPCA 2008Kjaergaard et al, JPCA 2008
10 Equilibrium constants Region(cm-1)Keq (atm-1)VPT2HCAO4.77 × 10-25.41 × 10-21.61 × 10-21.10 × 10-23.19 × 10-23.26 × 10-24.38 × 10-24.72 × 10-2Comparison of calculated (HCAO and VPT2) and observed vapor phase intensities in different regions cm-1 lead to Keq in the range to atm-1 at 298K
11 Water dimer in the atmosphere DvOH = 3½DvOH = 4H2O•H2O (calc)H2O (observed)Water dimer conc. depends on water conc. squared!115001310014750wavenumber (cm-1)Schofield, Kjaergaard, PCCP 2003
13 Ethylene GlycolDifferent conformers present at room temperature and seen in the overtone spectra.Hydrogen bonding(~58%)(~26%)(~10%)Small molecule, so high level ab initio calculations are possible: CCSD(T)/aug’-cc-pVTZ.Howard, Jørgensen, Kjaergaard, JACS 05.
14 Ethylene Glycol1f1b2f2bHigher overtones better but also more difficult!
15 Larger diolsPropanediol, and Butanediol have similar structures to Ethylene Glycol.EGQCISD/ G(2d,2p) calculations show stronger hydrogen bonding fromEG - PD - BD.Larger frequency red shiftsPDBDAO local mode calculation indicate similar intensities of bonded and free OH modes.Howard and Kjaergaard, JPC A 06.
16 OH-stretching in diols V=3V=4What happens to the hydrogen bonded OH-stretching vibrations?
17 Hydrated complexesVibrational band profile important for detection and effect.Kjaergaard, Robinson, Howard, Daniel, Headrick, Vaida, JPCA 2003
18 Water dimer, band profile Vibrational band profile important for detection and effect.Rotational profiles depend ondirection of TDMHfHbGarden, Halonen, Kjaergaard, JPCA 2008
19 Water dimer, band profile Effect of coupling to low frequency modes?Third CH-stretch overtone, p-xylene.108001100011200Adiabatic separation of methyl torsion and CH-stretching has explained CH-stretching overtone spectra in toluenes and xylenes.We can separate adiabatically, the fast OH-stretching motion from the slow intra-molecular motion.Rong, Kjaergaard, JPCA 2002
20 OO-stretch couplingUse variation in OH-stretch mode with OO displacement to construct effective OO-stretch potentialGarden, Halonen, Kjaergaard, JPCA 2008
21 OO-stretch coupling Shift in position of minimum. Both in s and E. Little change for OHf.Garden, Halonen, Kjaergaard, JPCA 2008
23 OO-stretch coupling Direction of TDM changed. HfDirection of TDM changed.HbOHb-stretching transition is wide, OHf-stretch is not.Garden, Halonen, Kjaergaard, JPCA 2008
24 Accepter wag couplingSeparate adiabatically, the fast OH-stretching motion from the slow acceptor wag motion.Garden unpublished
25 Accepter wag coupling Similar spreading of intensity. Closer to 1D transition.Double well changes order.<0|0><1|0>Garden unpublished
26 Water dimer, band profile Combining OH-stretch +OO-stretch +Acceptor wagFour moreintermolecular modes!Garden, unpublished
27 ConclusionThe local mode model gives a good description of the dominant OH-stretching overtone transitions.We can calculate quite accurate absolute overtone intensities ab initio for species that have not been observed.Guide experimental efforts to observe these species.Provide input for atmospheric impact studies.Water dimer band profile/width of OHb stretching transitions is very wide - making observation elusive - but increases impact on solar radiative transfer.
29 Acknowledgements Bryan R. Henry, Guelph Geoffrey R. Low Timothy W. RobinsonDaniel P. SchofieldJoseph R. LaneAnna L. GardenDaryl HowardBen MillerBryan R. Henry, GuelphVeronica Vaida, BoulderPoul Jørgensen, AarhusLauri Halonen, HelsinkiJohn Stanton, AustinBenny Gerber, IrvineKeith Shine, ReadingIgor Ptasnik, ReadingJohn S. Daniel, NOAAMARSDENFUND