Fourier transform spectra recorded using (a) natural abundance water vapor, (b) (H2O)-O-18-enriched water vapor, and (c) (H2O)-O-17-enriched water vapor are analyzed. The ratio of intensities in three spectra is used to identify 927 lines due to absorption by (H2O)-O-18. Intensities and self-broadening parameters are derived for these lines. Using theoretical linelists, comparisons with previously assigned (H2O)-O-16 spectra, and automatic searches for combination differences, 747 lines are assigned. These lines belong to 14 vibrational states in the 3nu + delta and 4nu polyads. Newly determined (H2O)-O-18 vibrational band origins include 4nu(1) at 13 793.09 cm(-1), 3nu(1) + nu(3) at 13 795.40 cm(-1), 2nu(1) + 2nu(3) at 14 188.82 cm(-1), nu(1) + 3nu(3) at 14 276.34 cm(-1), and 2nu(2) + 2nu(2) + nu(3) at 13 612.71 cm(-1). These results are compared with data in HITRAN. (C) 2002 Elsevier Science (USA)

Brault, JW

Tanaka, M

Tennyson, J

English

UCL Discovery

Absorption spectrum of H￿￿￿￿￿ O in the 12 400  14 520 cm￿￿ rangeMizuho TanakaDepartment of Physics and Astronomy, University College London, London WC1E 6BT, UKJames W. BraultLASP (Space Technology Building), 1234 Innovation Drive,Boulder, CO 80303­7814 U.S.A.Jonathan TennysonDepartment of Physics and Astronomy, University College London, London WC1E 6BT, UKE­mail: j.tennyson@ucl.ac.ukFouriertransformspectrarecordedusing(a)naturalabundancewater vapor, (b) H￿￿￿￿￿ O enriched water vapor and (c) H￿￿￿￿￿ O en­riched water vapor are analysed. The ratio of intensities in threespectra are used to identify 927 lines due to absorptions by H￿￿￿￿ O.Intensities and self­broadening parameters are derived for theselines. 778 linesareassigned usingtheoretical linelists,comparisonswithpreviouslyassignedH￿￿￿￿ Ospectraandautomaticsearchesforcombinationdifferences. Theselinesbelongto14vibrationalstatesinthe￿￿￿￿￿￿￿ and￿￿￿ polyads. NewlydeterminedH￿￿￿￿￿ Ovibrationalband origins include￿￿￿￿ at 13 793.09 cm￿￿ ,￿￿￿￿￿￿￿￿￿ at 13 795.40cm￿￿ ,￿￿￿￿￿￿￿￿￿￿￿ at 14 188.82 cm￿￿ ,￿￿￿￿￿￿￿￿￿ at 14 276.34 cm￿￿and￿￿￿￿￿￿￿￿￿￿￿￿￿ ￿!￿￿ at 13 612.71 cm￿￿ . These results are comparedwith data in HITRAN.1. INTRODUCTIONWater is well known as the major absorber of sunlight inthe Earth's atmosphere. Indeed water is so important that itssecond most abundant isotopomer, H"￿#%$ O, is considered to bethe fth most important absorber of solar radiation. Despite itsimportance the near­infrared and optical spectrum of H"#%$ O,key regions for atmospheric studies, remain poorly determined.In the early 1980s Chevillard and co­workers used the Mc­Math Fourier transform spectrometer at the National Solar Ob­servatory (Kitt Peak, AZ) to record spectra of isotopically en­riched water over wide frequency range. This experimentalwork resulted in a series of papers analysing the spectrum ofH"￿#%$ Ointherange440011500cm&￿# [1,2,3]. Morerecentlythis analysis has been extended up to 13 600 cm&￿# by Bykovet al [4]. In this work we extend the frequency range for whichthe H"￿#’$ O spectra are analysed up to 14 520 cm&￿# so that the(*),+.-and/)polyads are completely covered.Spectraofnaturalabundancewaterhasbeenextensivelystud­ied in the near­infrared and visible [5, 6, 7, 8, 9, 10, 11, 12, 13,14, 15]. Recently Schermaul et al [16] re­measured the spec­trumofnormalwaterusinga longpathlengthFouriertransformspectrometer belonging to the Molecular Structure Facility atRutherford Appleton Laboratory (UK) over the range 6 500 16 400 cm&￿# . For much of this range they probed signicantlydeeper than previous studies. In this work we use the spectra ofSchermauletaltoaidtheidenticationofdifferentisotopomers.2. EXPERIMENT DATAAs reported previously [1, 2, 3], Chevillard, Mandin, Flaudand Camy­Peyret measured the spectrum of two isotopicallyenriched samples of water using the McMath Fourier transformspectrometer. The rst sample contained H"￿#’$ O at0(,132%[2], refered to `#’$ O' below, and the second sample, `#%4 O' be­low, contained enhanced H"5#’4 O and H"￿#%$ O [3]. These spectra,which achieved a typical uncertainty in their line positions of0.001 cm&￿# [4], are publicly available via the Kitt Peak elec­tronicarchive. The#’$ O spectrumwas recordedusing 927scansand a pathlength of 434.0 m with a vapor pressure of 361.1 Pa.Lines in both spectra were tted in the 12 400  14 520 cm&6#rangeusingtheGREMLINprogram(Brault,unpublished). Theexact isotopic composition of these spectra is considered in de­tail below.To aid analysis of the isotopically enriched spectra we usedthe natural abundance, `#’7 O' below, Fourier Transform spec­trum of Schermaul et al [16]. For the frequency range 12 40012 M. TANAKA ET AL. 14 520 cm&￿# the#%7 O,#%$ O and#’4 O spectra were read into aspreadsheet and lines of the same frequency were aligned. Theintensities of these were ratioed giving characteristic patternswhich, for most lines and particularly for those appearing in allthreespectra, facilitated their identicationas belongto H"#%7 O,H"#%4 O or H"#%$ O. In this fashion 927 lines were denitely iden­tied as belonging to H"#%$ O. Parameters for these lines werethen extracted from the#%$ O spectrum and used for theoreticalanalysis. A complete list of these lines including intensities,scaled to natural abundance (see below) and self­broadeningparameters are given in the electronic archive.The exact isotopic composition of the#%$ O spectrum is ofcoursecrucial fordeterminingaccuratetransitionintensities. Inthis work we used the comparison between the three spectra todeterminethefactorbywhichthelinesofH"8#%$ Oareenhancedinthe#%$ Ospectrum. Todothisweusedthefollowinginformation:the total number of water molecules per cm&" in each sample,the abundance of each species in the#’7 O spectrum (assumed tobe natural abundance), the ratio of H"#%7 O linestrengths in the#’4 O and#%$ O spectra relative to the#%7 O spectrum, and the ratioH"#%4 O and H"#’$ O linestrengths in the#’4 O and#%$ O spectra.Thisproceduregivesthe ratioofH"#%$ O linestrengthsinthe#%$ Oto the#%7 O spectrum as 31.0 with an estimated error of 0.5. Italso shows that the abundance of H"￿#%4 O in the#%4 O spectrum,which is yet to be analysed, is fairly small at only about 3% ofthetotalwatercontent. Ourresultisconsistentwiththepreviousanalysis of Chevillard et al [2] whose published results can beused to give an enhancement of 30.7 with an error of 0.5. Thelinestrengthsgivenin the electronicarchivehave thereforebeendivided by 31.0 to scale them to natural abundance.3. ANALYSISSignicantadvanceshavebeenmadeintheanalysisofopticalspectra of water using variational calculations [12, 13, 17, 18].In this work a variety of strategies were adopted to analyse thespectra. At lower frequenciessome transitions, all belongingtothe(9):+;-polyad, had previously been assigned by Bykov etal [4], who studied H"#’$ O up to 13 600 cm&6# . Further `trivial'assignments, ones linking energy levels previously determinedexperimentally,could be made using the upper energy levels sogenerated.Initial assignments to new upper levels were then made bycomparison with variational H"5#’$ O line list generated by Par­tridge and Schwenke [17]. Although we were able to conrmmany of these assignments by combination differences, it be­came apparentby comparisonwith knownlevels of H"￿#’7 O [19]that in many cases the vibrational labels taken from the linelist were not correct. The transitions were therefore relabeledto obtain a consistent set of H"#%$ O energy levels. Particularlyhelpful in this regard was the ratio of H"#%$ O to H"#%7 O energylevels, which was found to be almost constant within a vibra­tional band and to only vary slightly between bands. Havingestablished the structure of the H"￿#%$ O levels in the region ofthe(*):+;-and/)polyad, further assignments were made bysearching for combination differences using a small computerprogram. This analysis leads to the assignment of 778 of the927 H"￿#%$ O lines. These assignments are given with the lines inthe electronic archive.Lines are assigned to 14 different upper vibrational levels.Threeof these, (013),(112)and(211),werealreadyextensivelystudied by Bykov et al [4]. The other states have not beenpreviously observed for H"#%$ O. Our new assignments can beused to characterize further H"#%$ O energy levels. Table 1 givesnewly derived energy levels for vibrational states (221), (400),(301), (202) and (103) which covers most of the new data. Forthese states, vibrational band origins have been determined at13612.71,13793.09,13795.4014188.82and14276.34cm&6#respectively. The small splitting between the (400) and (301)band origins shows, as has been noted previously [12], thatstretching states in the/)polyad for water are local­mode like.Table 1 therefore labels the vibrationalstates using both normalandlocalmodenotations. All ourlevels, including11for(023),9 for (122), 3 for (004) and one each for (141) and (042) aregiven in the electronic archive.4. DISCUSSION AND CONCLUSIONSA major reason for analysing the H"#’$ O spectra presentedhere is so that the data can be included in databases for usein atmospheric and other models. HITRAN [20] contains 47transitions assigned to H"￿#%$ O in the region studied here, whichare connedto the frequencyrange 13 608 13 893cm&6# . Thesource of these data is unknown to us. Our analysis conrmsthe assignments given in HITRAN, the only exceptions beingthe line at 13 847.279cm&6# , which we assign to(#%<>=?#" 301000 but whose assignment is mis­typed in HITRAN, and the/#A@B=C#’D line from the same band which we nd at 13 677.624cm&6# as opposed to 13 677.131cm&6# in HITRAN.Figure 1 compares the intensities given in HITRAN withthose derived here. For ease of analysis we plot the intensitiesfrom the#’$ O spectrum directly without scaling for enhancedH"#’$ O abundance. The ratio of our intensities to HITRAN is36.5117.3. This result is consistent with our result of 31.010.5. The almost 50 % error is well outside our error estimates,even when allowance is made for the errors in the individuallines, and it would appear therefore that the larger uncertaintymust be inherent to the HITRAN data.In this work we have used three separate long path lengthFourier transform spectra, recorded using water with differentisotopic composition,to identify lines belongingto H"5#’$ O. 927lines have been so identied and 778 of them assigned using avariety of techniques. Comparison with known data for H"￿#%7 Oaided this process. The spectra analysed here include one con­taining enhanced H"#’4 O. It should be possible to apply thetechniques used here to this spectrum.ACKNOWLEDGMENTSWe thank Roman Tolchenov and Nikolai Zobov for helpfuldiscussion during the course of this work. This work was sup­ABSORPTION SPECTRUM OF H￿￿￿￿ O 3portedinpartbytheUKNaturalEnvironmentResearchCounciland the UK Engineering and Science Research Council.REFERENCES1. J. P. Chevillard, J.­Y. Mandin, J.­M. Flaud and C. Camy­Peyret, Can. J.Phys., 63, 1112­1127 (1985).2. J. P. Chevillard, J.­Y. Mandin, J.­M. Flaud and C. Camy­Peyret, Can. J.Phys., 64, 746­761 (1986).3. J. P. Chevillard, J.­Y. Mandin, J.­M. Flaud and C. Camy­Peyret, Can. J.Phys., 65, 777­789 (1987).4. A.Bykov,O.Naumenko,T.Petrova,A.Scherbakov,L.Sinitsa,J.Y.Mandin,C.Camy­Peyret and J.­M.Flaud, J. Molec. Spectrosc., 172, 243­253 (1995).5. C. Camy­Peyret, J.­M. Flaud, J.­Y. Mandin, J.­P. Chevillard, J. Brault,D. R. Ramsay and M. Vervloet, J. Mol. Spectrosc. 113, 208­228 (1985).6. J.­Y. Mandin, J.­P. Chevillard, C. Camy­Peyret and J.­M. Flaud, J. Mol.Spectrosc. 116, 167­190 (1986).7. J.­Y. Mandin, J.­P. Chevillard, J.­M. Flaud and C. Camy­Peyret, Can. J.Phys. 66, 997­1011 (1988).8. J.­P. Chevillard, J.­Y. Mandin, J.­M. Flaud and C. Camy­Peyret, Can. J.Phys. 67, 1065­1084 (1989).9. R. A. Toth, J. Mol. Spectrosc. 166, 176­183 (1994).10. J.­M. Flaud, C. Camy­Peyret, A. Bykov, O. Naumenko, T. Petrova,A. Scherbakov and L. 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(2002).17. H. Partridge and D. W. Schwenke, J. Chem. Phys. 106, 4618­4639 (1997).18. O. L. Polyansky, N. F. Zobov, S. Viti and J. Tennyson, J. Mol. Spectrosc.189, 291­300 (1998).19. J.Tennyson, N. F.Zobov,R. Williamson, O.L.Polyansky and P.F.Bernath,J. Phys. Chem. Ref. Data, 30, 735­831 (2001).20. L. S. Rothman, C. P. Rinsland, A. Goldman, S. T. Massie, D. P. Ed­wards, J.­M. Flaud, A. Perrin, C. Camy­Peyret, V. Dana, J.­Y. Mandin,J. Schroeder, A. McCann, R. R. Gamache, R. B. Wattson, K. Yoshino,K. V. Chance, K. W. Jucks, L. R. Brown, V. Nemtchinov and P. Varanasi, J.Quant. Spectrosc. Radiat. Transfer 60, 665­710 (1998); for HITRAN2000see www.hitran.com.FIGURE CAPTIONSFigure1RatioofH"￿#%$ Olineintensitiesobtainedinthiswork(unscaled for isotopic enrichment) to those given in HITRAN[20].

Absorption spectrum of (H2O)-O-18 in the range 12 400-14 520 cm(-1)

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