Theoretical work on thewater monomer and dimer

Matt BarberJonathan TennysonUniversity College London

matt@theory.phys.ucl.ac.uk

December 2008

Outline of work so far

Improvements to water line list Extended to cover 800-19,600 cm-1

New sources added

Partition function for water dimer Few energy levels filled at low temperatures Most dimers are in the ground vibrational state Rotational levels convergent up to 20K No useful published comparisons

Line lists for 11000-19500 cm-1

HITRAN Good reference for strong lines

BT2 R J Barber and Jonathan Tennyson, UCL Theoretical model with experimentally determined energy levels.

Retrofitted experimental spectra Tolchenov R, Tennyson J: "Water line parameters from refitted

spectra constrained by empiricalupper state levels: study of the 9500-14500 cm-1 region". JQSRT, 109(4), 559-568 (2008).

Grenoble data Very accurate measurements using cavity ring down spectroscopy Comparatively clean area for HITRAN lines

Sources available in 11000 cm-1 to 19000 cm-1 region

0

1

2

3

4

11000 12000 13000 14000 15000 16000 17000 18000 19000

Frequency / cm-1

GRENOBLE

IMPERIAL

HITRAN

BT2

Line lists for 750-7500 cm-1

Coudert The H216O molecule: Line position and line intensity analyses up to the second triad,

L.H. Coudert, G. Wagner, M. Birk, Yu.I. Baranov, W.J. Lafferty, J.-M. Flaud, JMS (preprint 2008)

Brussels-Reims Fourier transform measurements of water vapor line parameters in the 4200-

6600 cm-1 region, Jenouvrier, A; Daumont, L; Regalia-Jarlot, L, et al., JQSRT (105/2. pp 326-355, 2007)

Giessen Water vapor absorption line intensities in the 1900-6600 cm-1 region, Mikhailenko,

SN; Albert, KAK; Mellau, G, et al., JQSRT  (109/16, pp2687-2696, 2008)

Grenoble Weak water absorption lines around 1.455 and 1.66 mu m by CW-CRDS,

Mikhailenko, SN; Le, W; Kassi, S, et al., JMS (244/2, pp170-178, 2007)

Sources available in 750 cm-1 to 7500 cm-1 region

0

1

2

3

4

0 1000 2000 3000 4000 5000 6000 7000 8000

Frequency / cm-1

GRENOBLE

COUDERT

GIESSEN

JENOUVRIER

HITRAN/SISAM/TOTH

BT2

BT2 compared with HITRAN

-0.1

-0.08

-0.06

-0.04

-0.02

0

0.02

0.04

0.06

0.08

0.1

-25 -24 -23 -22 -21 -20 -19 -18

log intensity

log r

atio

(B/H

)

Coudert compared with BT2

-0.1

-0.08

-0.06

-0.04

-0.02

0

0.02

0.04

0.06

0.08

0.1

-25 -24 -23 -22 -21 -20 -19 -18

log intensity

log ra

tio (B

/C)

Comparison of HITRAN and UCL line lists

0

4E-27

8E-27

1.2E-26

1.6E-26

2E-26

817 817.5 818 818.5 819 819.5 820 820.5 821 821.5 822

Frequency / cm-1

Inte

sity

/ cm

mol

-1

HITRAN

UCL

Dimer partition function at 20K

Only lowest vibrational state occupied Rotational states up to J=20 occupied Statistical weights g from Groenemboom et

al. G

16 Symmetry

Equation:

gJeTQ kT

Ehc

)12()(

0 5 10 15 20 25 30 35 40 45 500

250500750

100012501500175020002250250027503000325035003750

Differing numbers of states

4

3

2

1

T / K

Parti

tion

Sum

0 5 10 15 20 25 30 35 40 45 500

250500750

100012501500175020002250250027503000325035003750

Differing maxJ values

J<21

J<18

J<15

J<12

J<9

T/K

Parti

tion

Sum

Conclusion

Monomer linelist Now covering from Submit to BADC? Publish?

Dimer partition function Convergent at 20K Reasonable at 50K Need many more levels for room temperature No low temperature comparisons available