The influence of water vapor absorption in the nm region on solar radiance: Laboratory studies and model simulation

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1 GEOPHYSICAL RESEARCH LETTERS, VOL. 40, , doi: /grl.50935, 2013 The influence of water vapor absorption in the nm region on solar radiance: Laboratory studies and model simulation Juan Du, 1 Li Huang, 1 Qilong Min, 2 and Lei Zhu 1,3 Received 8 August 2013; revised 27 August 2013; accepted 6 September 2013; published 13 September [1] Water vapor is an important greenhouse gas in the Earth s atmosphere. Absorption of solar radiation by water vapor in the near-uv region may partially account for up to 30% discrepancy between the modeled and the observed solar energy absorbed by the atmosphere. But the magnitude of water vapor absorption in the near-uv region at wavelengths shorter than 384 nm is not known. We have determined absorption cross sections of water vapor at 5 nm intervals in the nm region, by using cavity ring-down spectroscopy. Water vapor cross-section values range from to cm 2 /molecule in the wavelength region studied. The effect of the water vapor absorption in the nm region on the modeled radiation flux at the ground level has been evaluated using radiative transfer model. Citation: Du, J., L. Huang, Q. Min, and L. Zhu (2013), The influence of water vapor absorption in the nm region on solar radiance: Laboratory studies and model simulation, Geophys. Res. Lett., 40, , doi: /grl Introduction [2] Water vapor is a major absorber of solar radiation and plays a central role in climate change and radiative balance of the atmosphere [Houghton et al., 2001]. It is well known that water vapor has far UV electronic absorption band [Okabe, 1978], strong IR absorption bands [Rothman et al., 2009; Tennyson et al., 2013], and visible overtone absorption bands [Rothman et al., 2009; Tennyson et al., 2013]. Water vapor overtone absorption bands were measured previously at wavelengths longer than nm [Bernath, 2002; Carleer et al., 1999; Coheur et al., 2001, 2002; Camy-Peyret et al., 1985; Mandin et al., 1986; Flaud et al., 1997; Polyansky et al., 1998; Jensen, 1989; Zobov et al., 2000; Dupré et al., 2005]. In addition to the single photon absorption bands at λ nm, multiphoton excitation spectra of water vapor [Grechko et al., 2008, 2009; Maksyutenko et al., 2006, 2007] were measured at selected wavelengths in the UV region. Although energy levels of the highly vibrationally excited water molecules up to the dissociation limit have been 1 Wadsworth Center, New York State Department of Health, Albany, New York, USA. 2 Atmospheric Sciences Research Center, State University of New York at Albany, Albany, New York, USA. 3 Department of Environmental Health Sciences, State University of New York at Albany, Albany, New York, USA. Corresponding author: L. Zhu, Wadsworth Center, New York State Department of Health and Department of Environmental Health Sciences, State University of New York at Albany, Albany, NY 12201, USA. (zhul@wadsworth.org) American Geophysical Union. All Rights Reserved /13/ /grl calculated [Zobov et al., 2000; Li and Guo, 2001; Bačić et al., 1988; Choi and Light, 1992; Partridge and Schwenke, 1997; Mussa and Tennyson, 1998;Gray and Goldfield, 2001; Polyansky et al., 2003; Császár et al., 2010], there has been no reported experimental study of the single photon absorption spectrum of water vapor at wavelengths shorter than nm in the near-uv region. [3] Obtaining absorption cross sections of highly vibrationally excited water molecules as a function of wavelength in the near-uv range is experimentally challenging as water vapor absorptions are very weak. Due to the large number of vibrational density of states of water vapor (268 predicted vibrational bands [Császár et al., 2010]) in the nm region and extensive state mixing, even the accurate prediction of energy levels for highly vibrationally excited water molecules had been a major challenge for theoretical chemists until very recent years [Zobov et al., 2000; Li and Guo, 2001]. Absorption of the solar radiation by water vapor in the near-uv region may partially account for the up to 30% discrepancy between the modeled and the observed solar energy absorbed by the atmosphere [Arking, 1996, 1999; Li et al., 1997; Wild et al., 1995; Cess et al., 1995; Zhong et al., 2001; Bai, 2009]. Determination of the water vapor absorption cross sections in the near-uv region is necessary in order to obtain appropriate modeling of the atmospheric radiation over the full solar spectrum. [4] Under atmospheric conditions, water vapor scattering effect is small. Based on literature data on water vapor scattering studies [Sutton and Driscoll, 2004; Tomasi et al., 2005], the estimated scattering cross sections of water vapor are on the order of to cm 2 /molecule over the nm range. Reported in this paper are gas phase absorption cross sections of H 2 O determined at 5 nm intervals in the nm region using highly sensitive cavity ring-down spectroscopy [O Keefe and Deacon, 1988; O Keefe et al., 1990]. The effect of water vapor near- UV absorption on the radiation flux at the ground level has been evaluated using radiative transfer model. 2. Experimental [5] The near-uv absorption cross sections of water vapor ( nm) were measured using cavity ring-down spectroscopy. Detailed descriptions of the experimental setup can be found elsewhere [Zhu and Johnston, 1995; Zhu and Ding, 1997; Zhu and Kellis, 1997]. The probe laser source for the cavity ring-down spectrometer was the fundamental or the second harmonic output of a dye laser pumped by a 308 nm excimer laser. Laser dyes used to cover the nm range were rhodamin 6G, rhodamin B, rhodamin 101, 4-dicyanomethylene-2-methyl-6-p-dimethylaminostyryl-4H-pyran (DCM), and p-terphenyl (PTP). The pulse energy of the

2 Figure 1. (a) Roundtrip extinction at 330 nm as a function of the H 2 O pressure in the cell. The solid line is a linear least squares analysis of the experimental data and (b) gas phase H 2 O absorption cross section as a function of the wavelength in the nm region. ring-down probe beam was <0.25 mj/pulse. The stainless steel cell was vacuum-sealed by a pair of high-reflectance cavity mirrors. The ring-down probe beam was directed along the main optical axis of the cell. A fraction of the probe beam was injected into the cavity through the front mirror. The probe beam inside the cavity decayed as a result of mirror transmission loss and sample absorption/scattering. The photon intensity decay inside the cavity was monitored via measurement of the weak transmission of light through the rear mirror with a photomultiplier tube (PMT). The PMT output was amplified, digitized, and sent to a computer. The decay curve was fitted to a single-exponential decay function, from which the ring-down time constant (τ) and the total loss (Γ) per roundtrip pass were extracted. [6] Liquid water sample was purified by pumping the deionized water for 30 min to remove dissolved air. The stainless steel cell wall was thoroughly cleaned with acetone; the cell was heated and simultaneously pumped using a diffusion pump for an extended period of time to further degas chamber walls. Gas pressure was measured at the center of the cell by an MKS 622A Baratron capacitance manometer (10 Torr maximum scale, measurement uncertainty is 0.25% of the pressure reading). Absorption/scattering of the probe beam by water vapor was determined under static conditions at 293 ± 2 K. 3. Results and Discussion 3.1. Absorption Cross Sections of Water Vapor in the nm Region [7] We have determined the near-uv extinction cross sections of water vapor at 5 nm intervals in the nm region by using cavity ring-down spectroscopy. Displayed in Figure 1a is roundtrip extinction obtained at 330 nm as a function of the H 2 O pressure in the cell. As seen from Figure 1a, extinction increases with water vapor pressure for up to 10 Torr pressure. Fitting of the experimental data using a linear least squares analysis yielded a water vapor extinction cross section of cm 2 /molecule at 330 nm. The literature scattering cross section of water vapor [Sutton and Driscoll, 2004; Tomasi et al., 2005] is on the order of cm 2 /molecule at 330 nm, which is at least three orders of magnitude smaller than the H 2 O extinction cross section at this wavelength. Water vapor scattering contribution is negligible and an H 2 O absorption cross section of cm 2 /molecule was obtained at 330 nm. We also determined water vapor absorption cross sections at other wavelengths in the nm region (H 2 O absorption cross sections in the nm region are too small to be accurately measured). The H 2 O crosssection values are listed in Table 1 and plotted in Figure 1b. Water vapor cross-section values range between (2.94 ± 0.11) and (2.13 ± 0.22) cm 2 /molecule over the nm range, where errors quoted represents 1σ scatter from three repeated measurements. Gas phase absorption spectrum of H 2 O over the nm range exhibits major absorption maxima at 290, 315, and 330 nm, and a minor absorption maximum at 345 nm. Li and Guo [2001] calculated energy levels of the highly vibrationally excited water molecules. The calculated stretching overtone bands are peaked at nm for (10,0) ± 0, nm for (11,0) ± 0, and nm for (12,0) ± 0, where (n,m) ± b is local mode notation in which n and m denote the stretching quanta in OH bonds, b denotes the bending quanta, and ± refers to symmetric/antisymmetric combination. Li and Guo [2001] did not calculate H 2 O near-uv band intensity. In harmonic model of molecular vibrations, the intensity of the nth overtone Table 1. Gas Phase Absorption Cross Sections of H 2 Ointhe nm Region a λ (nm) σ (cm 2 /molecule) 290 (2.27 ± 0.18) (1.06 ± 0.05) (8.71 ± 0.33) (6.85 ± 0.13) (5.58 ± 0.79) (2.19 ± 0.11) (1.62 ± 0.03) (1.40 ± 0.03) (2.94 ± 0.11) (5.89 ± 0.37) (2.49 ± 0.45) (4.80 ± 0.69) (2.13 ± 0.22) a Errors quoted represent 1σ scatter from three repeated cross-section measurements. 4789

3 depends on the (n + 1)th derivative of the dipole surface; the best dipole moment surfaces [Lodi et al., 2008; Schwenke and Patridge, 2000] available to water have been found [Császár et al., 2010] to give unreliable tenth or higher derivatives in the region of equilibrium geometry. Maksyutenko et al. [2007] measured OH fragment laser-induced fluorescence (LIF) spectrum following multiphoton excitation of water vapor beyond the dissociation limit. They used a photon from the first laser to promote water molecules to an intermediate level followed by using a photon from the second laser to promote a fraction of preexcited water molecules to a higher rovibrational level containing 8 12 OH stretch quanta and 0 1 OH bend quanta; they subsequently applied a photon from the third laser to excite water molecules to the repulsive A 1 B 1 electronic state followed by detecting OH fragment with LIF. Rotational selection rules governing each overtone excitation step allowed Maksyutenko et al. [2007] to select J = 1 rotational level to do spectroscopic study. The two-step excitation scheme allowed multiphoton excitation study to be carried out at H 2 O pressures in the mtorr range. Maksyutenko et al. [2007] made the following band origin assignments for water vapor: nm for (7,1) ± 2, nm for (9,0) ± 1, nm for (10,0) ± 0, nm for (9,1) ± 0, nm for (10,0) ± 1, nm for (11,0) ± 0, nm for (11,0) ± 1, and nm for (12,0) ± 0. But they did not provide information about band intensity. One should be cautioned when comparing peak positions in our water vapor spectrum shown in Figure 1b with band origins from H 2 O multiphoton excitation study as we did not target band origins in our experiments. We measured water vapor absorption from a Boltzmann distribution of rotational states. Since there are 268 predicted vibrational bands [Császár et al., 2010] for water vapor in the nm region, the cross-section values we obtained are ensemble average cross-section values from all the water vapor rovibrational states that absorb at a given wavelength. On the other hand, literature multiphoton band origin study was carried out under collisionless condition at mtorr H 2 O pressure and a preselected J = 1 rotational level. That can explain why our water vapor spectrum is so spread out, and why comparing wavelengths at which absorption maxima occur in our near-uv water vapor spectrum to band origins from literature water vapor multiphoton excitation study could become irrelevant. [8] One may wonder how accurate these ultraweak water vapor cross-section data are. Indeed, determination of the absorption cross sections of water vapor in the near-uv region is challenging experimentally not only because the measured absorptions are small but also because tiny amount of highly UV-absorbing impurity would result in inflated water vapor cross-section values. To test our ability to determine weak cross-section values, we measured absorption as a function of water vapor pressure in the 1 10 Torr range for a rovibrational line at nm (22587 cm 1 ). We obtained a water vapor cross-section value of (1.92 ± 0.47) cm 2 / molecule, which agrees with that of cm 2 /molecule reported by Coheur et al. [2001]. We have taken painstaking efforts to remove tiny amount of UV-absorbing impurity such as halocarbon wax from the chamber wall, which was found to be the largest interference in the water vapor near- UV cross-section measurements. An inductively coupled plasma mass spectrometry (ICP-MS) analysis of our liquid water sample showed that metal ion concentrations were below ppb level and our water sample was pure. To get rid of dissolved air in water, we purified the water either by repeated freeze-pump-thaw cycles or by pumping liquid water for 30 min; we obtained similar water vapor cross-section value using either method. One may wonder if water dimer absorption in the near-uv region may contribute to the measured water vapor absorption. Literature water dimer formation equilibrium constant [Shillings et al., 2011; Temelso et al., 2011] is around 0.05 atm 1 at 293 K. Only 0.066% of water vapor exists as water dimer at 10 Torr pressure. In addition, water dimer absorption is expected to have a quadratic dependence on water vapor pressure. Water vapor absorptions we obtained in the near-uv region did not show quadratic dependence on water vapor pressure in the 1 10 Torr range. The low water dimer percentage at 10 Torr water vapor pressure and the absence of quadratic dependence of absorption on water vapor pressure let us conclude that water dimer had negligible interference in water vapor cross-section measurements. One may also wonder if water vapor may adsorb on cavity mirrors, and if adsorbed water could interfere with water vapor crosssection measurements. The surfaces of the cavity mirrors were super polished. We did not observe water vapor adsorption on cavity mirrors until water vapor pressure inside the cell was about 15 Torr. In a separate study, we directly measured absorption cross sections of surfaceadsorbed water in the nm region [Du et al., 2013]; water vapor surface cross-section values are about four orders of magnitude larger than H 2 O gas phase crosssection values in the nm region. We should be able to detect water vapor adsorption on cavity mirrors should this process happen, but we found no evidence for water vapor adsorption on cavity mirrors for H 2 O pressures over the 1 10 Torr range. We can exclude adsorbed water on cavity mirrors as interference in water vapor cross-section measurements. We thoroughly cleaned the cavity mirrors before each experiment. All of these cautionary measures were taken to ensure that our cross-section data in the nm region are indeed those of water vapor Effect of Water Vapor Absorption in the nm Region on the Modeled Radiation Flux at the Ground Level [9] To evaluate the effect of water vapor near-uv absorption on radiative flux at the ground, we incorporated the measured water vapor absorption cross sections into the atmospheric radiative transfer model using moderate resolution atmospheric transmission (MODTRAN) [Berk et al., 1989]. We linearly interpolated the water vapor cross-section data at 5 nm interval in the nm region to the MODTRAN resolution. We used MODTRAN middle-latitude summer atmosphere, with total ozone of 330 Dobson unit and total water vapor amount of 14 mm. For this standard atmosphere, the optical depth of water vapor absorption is larger than that of ozone absorption at wavelengths longer than 340 nm (see Figure 2a). The water vapor absorption depth is smaller than ozone Huggins absorption depth at wavelengths shorter than 320 nm. Over the nm range, ozone absorption optical depth changes from being frequently larger to being frequently smaller than water vapor absorption optical depth. For radiation simulation, we set the aerosol optical depth of 0.1 at 320 nm, the solar zenith angle of 55, and the surface albedo of MODTRAN-simulated radiations show significant differences with/without water vapor 4790

4 Figure 2. (a) Optical depth spectra of total, water vapor, ozone, and aerosols; (b) MODTRAN-simulated surface radiation spectra of direct and diffuse beam with/without water vapor absorption; and (c) Corresponding difference (%) with/without water vapor absorption. absorption, in the range of 2% 22%, in direct beam and diffuse radiation at the ground (Figures 2b and 2c). The difference in the modeled direct or diffuse radiance at the ground with/without water vapor near-uv absorption amounts to 10% 16% at 290 nm, about 16% at 315 nm, and about 22% at 330 nm. Although the dominant radiative forcing in the nm region is ozone absorption, the contribution of additional water vapor absorption is about 0.5 W/m 2 or 1% in the region. Ozone concentration is higher in the upper troposphere than in the lower troposphere; ozone absorption affects solar radiation mostly in the upper troposphere. Water vapor is mainly confined in the lower troposphere; water vapor near-uv absorption is expected to impact the solar flux and radiative heating mostly in the lower troposphere. Thus, H 2 OandO 3 have different radiative heating profiles. Water vapor near-uv absorption is not expected to photodissociate water molecules as the dissociation threshold [Maksyutenko et al., 2006] for overtone excitation is 243 nm. Attributing uncertainty in the field-measured water vapor near-uv absorption to uncertainty in the field-measured tropospheric ozone absorption would overestimate the contribution of ozone photolysis in the troposphere. [10] We have examined the impact of water vapor near- UV absorption on the modeled radiative flux at the ground. Over the full spectrum range of solar radiation, the estimated peak optical depths of water vapor are about 0.14, 0.49, 0.72, 2.9, and 4.3 in the nm, nm, nm, nm, and nm regions, respectively, where values of peak optical depth are based on the MODTRAN resolution of 2 cm 1. Thus, the dominant absorber of solar radiation is still water vapor in the infrared region. 4. Conclusions [11] In this paper, we report measurements of the near-uv absorption cross sections of water vapor in the nm region by using cavity ring-down spectroscopy. Our water vapor cross-section data are expected to provide experimental feedback necessary for the development of accurate theoretical dipole moment potential energy surfaces that can predict band intensities for highly vibrationally excited water. Water vapor cross-section values range from to cm 2 /molecule in the wavelength region studied. By coupling experimental water vapor cross-sectiondatawithmodelingofthesolarflux at the 4791

5 ground using radiative transfer model, we have shown that water vapor absorption in the nm region can cause significant differences (up to 22%) in both the direct beam and the diffuse radiation at the ground. The model simulation was made by interpolating water vapor cross-section data determined at 5 nm intervals in the nm region. Given that water vapor near-uv absorption spectrum is structured, it is necessary to measure the near-uv absorption cross sections of water vapor at narrower wavelength intervals to gauge the full impact of water vapor near-uv absorption toward the energy balance of the atmosphere and toward the climate. [12] Acknowledgments. We thank Chris Judd for performing ICP-MS analysis of the deionized water sample and for many discussions. Discussions with Liang T. Chu, Theodore Dibble, and Richard Cole are also acknowledged. We are grateful for the support provided by the National Science Foundation under grant AGS [13] The Editor thanks Jonathan Tennyson and an anonymous reviewer for their assistance in evaluating this paper. References Arking, A. (1996), Absorption of solar energy in the atmosphere: Discrepancy between model and observations, Science, 273, Arking, A. (1999), The influence of clouds and water vapor on atmospheric absorption, Geophys. Res. Lett., 26, Bačić, Z., D. Watt, and J. C. Light (1988), A variational localized representation calculation of the vibrational levels of the water molecule up to cm 1, J. Chem. Phys., 89, Bai, J. H. (2009), UV attenuation in the cloudy atmosphere, J. Atmos. Chem., 62, Berk, A., L. S. Bernstein, and D. C. Robertson (1989), MODTRAN: A Moderate Resolution Model for LOWTRAN7, Rep. AFGL-TR , Air Force Geophys. Lab., Hanscom, AFB, Ma. Bernath, P. F. (2002), Water vapor gets excited, Science, 29, Camy-Peyret, C., J.-M. Flaud, J.-Y. Mandin, J.-P. Chevillard, J. Brault, D. A. Ramsay, M. Vervloet, and J. Chauville (1985), The high-resolution spectrum of water vapor between and cm 1, J. Mol. Spectrosc., 113, Carleer, M., A. Jenouvrier, A. C. Vandaele, P. F. Bernath, M. F. Merienne, R. Colin, N. F. Zobov, O. L. Polyansky, J. Tennyson, and V. A. Savin (1999), The near infrared, visible, and near ultraviolet overtone spectrum of water, J. Chem. Phys., 111, Cess, R. D., et al. (1995), Absorption of solar radiation by clouds: Observations versus models, Science, 267, Choi, S. E., and J. C. Light (1992), Highly excited vibrational eigenstates of nonlinear triatomic molecules. Application to H 2 O, J. Chem. Phys., 97, Coheur, P.-F., S. Fally, A. C. Vandaele, C. Hermann, A. Jenouvrier, M. Carleer, M.-F. Mérienne, C. Clerbaux, and R. Colin (2001), Absolute intensities of water vapor lines in the near ultraviolet and visible regions, Proc SPIE, 4168, Coheur, P. F., S. Fally, M. Carleer, C. Clerbaux, R. Colin, A. Jenouvrier, M. F. Merienne, C. Hermans, and A. C. Vandaele (2002), New water vapor line parameters in the cm 1 region, J. Quant. Spectrosc. Radiat. Transfer, 74, Császár, A. G., E. Mátyus, T. Szidarovszky, L. Lodi, N. F. Zobov, S. V. Shirin, O. L. Polyansky, and J. Tennyson (2010), First-principles prediction and partial characterization of the vibrational states of water up to dissociation, J. Quant. Spectrosc. Radiat. Transfer, 111, Du, J., L. Huang, and L. Zhu (2013), Absorption cross sections of surfaceadsorbed H 2 O in the nm region and heterogeneous nucleation of H 2 O on fused silica surfaces, J. Phys. Chem. A, doi: /jp405573y. Dupré, P., T. Gherman, N. F. Zobov, R. N. Tolchenov, and J. Tennyson (2005), Continuous-wave cavity ringdown spectroscopy of the 8ν polyad of water in the cm 1 range, J. Chem. Phys., 123, 154,307. Flaud, J.-M., C. Camy-Peyret, A. Bykov, O. Naumenko, T. Petrova, A. Scherbakov, and L. Sinitsa (1997), The high-resolution spectrum of water vapor between and cm 1, J. Mol. Spectrosc., 183, Gray,S.K.,andE.M.Goldfield (2001), Highly excited bound and Lowlying resonance states of H 2 O, J. Phys. Chem. A, 105, Grechko, M., P. Maksyutenko, N. F. Zobov, S. V. Shirin, O. L. Polyansky, T. R. Rizzo, and O. V. Boyarkin (2008), Collisionally assisted spectroscopy of water from cm 1, J. Phys. Chem. A, 112, 10,539 10,545. Grechko, M., O. V. Boyarkin, T. R. Rizzo, P. Maksyutenko, N. F. Zobov, S. V. Shirin, L. Lodi, J. Tennyson, A. G. Császár, and O. L. Polyansky (2009), State-selective spectroscopy of water up to its first dissociation limit, J. Chem. Phys., 131, 221,105, doi: / Houghton, J. T., Y. Ding, D. J. Griggs, M. Noguer, P. J. Van der Linden, X. Dai, K. Maskell, and C. A. Johnson (2001), Climate Change 2001: The Scientific Basis, Cambridge University Press, Cambridge. Jensen, P. (1989), The potential energy surface for the electronic ground state of the water molecule determined from experimental data using a variational approach, J. Mol. Spectrosc., 133, Li, G., and H. Guo (2001), The vibrational level spectrum of H 2 O(X 1A ) from the Partridge-Schwenke potential up to the dissociation limit, J. Mol. Spectrosc., 210, Li, Z., L. Moreau, and A. Arking (1997), On solar energy disposition: A perspective from observation and modeling, Bull. Am. Meteorol. Soc., 78, Lodi, L., R. N. Tolchenov, J. Tennyson, A. E. Lynas-Gray, S. V. Shirin, N. F. Zobov, O. L. Polyansky, A. G. Császár, J. N. P. van Stralen, and L. Visscher (2008), A New ab initio ground-state dipole moment surface for the water molecule, J. Chem. Phys., 128, 044,304. Maksyutenko, P., T. R. Rizzo, and O. V. Boyarkin (2006), A direct measurement of the dissociation energy of water, J. Chem. Phys., 125, 181,101. Maksyutenko, P., J. S. Muenter, N. F. Zobov, S. V. Shirin, O. L. Polyansky, T. R. Rizzo, and O. V. Boyarkin (2007), Approaching the full Set of energy levels of water, J. Chem. Phys., 126, 241,101. Mandin, J.-Y., J.-P. Chevillard, C. Camy-Peyret, J.-M. Flaud, and J. W. Brault (1986), The high-resolution infrared spectrum of water vapor between and cm 1, J. Mol. Spectrosc., 116, Mussa, H. Y., and J. Tennyson (1998), Calculation of the rotation vibration states of water up to dissociation, J. Chem. Phys., 109, 10,885 10,892. Okabe, H. (1978), Photochemistry of Small Molecules, John Wiley and Sons, New York, NY. O Keefe, A., and D. A. G. Deacon (1988), Cavity ring-down optical spectrometer for absorption measurements using pulsed laser sources, Rev. Sci. Instrum., 59, O Keefe,A.,J.J.Scherer,A.L.Cooksy,R.Sheeks,J.Heath,andR.J.Saykally (1990), Cavity ring down dye laser spectroscopy of jet-cooled metal clusters: Cu 2 and Cu 3, Chem. Phys. Lett., 172, Partridge, H., and D. W. Schwenke (1997), The determination of an accurate isotope dependent potential energy surface for water from extensive ab initio calculations and experimental data, J. Chem. Phys., 106, Polyansky, O. L., N. F. Zobov, S. Viti, and J. Tennyson (1998), Water vapor line assignments in the near infrared, J. Mol. Spectrosc., 189, Polyansky, O. L., A. G. Császár, S. V. Shirin, N. F. Zobov, P. Barletta, J. Tennyson, D. W. Schwenke, and P. J. Knowles (2003), High-accuracy ab initio rotation-vibration transitions for water, Science, 299, Rothman, L. S., et al. (2009), The HITRAN 2008 molecular spectroscopic database, J. Quant. Spectrosc. Radiat. Transfer, 110, Schwenke, D. W., and H. Patridge (2000), Convergence testing of the analytic representation of an ab initio dipole moment function for water: Improved fitting yields improved intensities, J. Chem. Phys., 113, Shillings, A. J. L., S. M. Ball, M. J. Barber, J. Tennyson, and R. L. Jones (2011), An upper limit for water dimer absorption in the 750 nm spectral region and a revised water line list, Atmos. Chem. Phys., 11, Sutton, J. A., and J. F. Driscoll (2004), Rayleigh scattering cross sections of combustion species at 266, 355, and 532 nm for thermometry applications, Opt. Lett., 29, Temelso, B., K. A. Archer, and G. C. Shields (2011), Benchmark structures and binding energies of small water clusters with anharmonicity corrections, J. Phys. Chem. A, 115, 12,034 12,046. Tennyson, J., et al. (2013), IUPAC critical evaluation of the rotational-vibrational spectra of water vapor, part III: Energy levels and transition wavenumbers for H 2 16 O, J. Quant. Spectrosc. Radiat. Transfer, 117, Tomasi, C., V. Vitale, B. Petkov, A. Lupi, and A. Cacciari (2005), Improved algorithm for calculations of Rayleigh-scattering optical depth in standard atmospheres, Appl. Opt., 44, Wild, M., A. Ohmura, H. Gilgen, and E. Roeckner (1995), Validation of general circulation model radiative fluxes using surface observations, J. Clim., 8, Zhong, W., J. D. Haigh, D. Belmiloud, R. Schermaul, and J. Tennyson (2001), The impact of new water vapour spectral line parameters on the calculation of atmospheric absorption, Q. J. R. Meteorol. Soc., 127, Zhu, L., and C.-F. Ding (1997), Temperature dependence of the near UV absorption spectra and photolysis products of ethyl nitrate, Chem. Phys. Lett., 265, Zhu, L., and G. Johnston (1995), Kinetics and products of the reaction of the vinoxy radical with O 2, J. Phys. Chem., 99, 15,114 15,119. Zhu, L., and D. Kellis (1997), Temperature dependence of the UV absorption cross sections and photodissociation products of C 3 -C 5 alkyl nitrates, Chem. Phys. Lett., 278, Zobov, N. F., et al. (2000), The near ultraviolet rotation-vibration spectrum of water, J. Chem. Phys., 113,