theoretical work on the water monomer and dimer matt barber jonathan tennyson university college...
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Theoretical work on thewater monomer and dimer
Matt Barber
Jonathan Tennyson
University College London
13th May 2010
0.0E+00
5.0E-09
1.0E-08
1.5E-08
2.0E-08
2.5E-08
3.0E-08
3.5E-08
4.0E-08
4.5E-08
5.0E-08
606 608 610 612 614 616 618 620 622
Wavelength / nm
Ab
sorp
tio
n C
oef
fici
ent
/ cm
-1
Measured
UCL '08
0.0E+00
5.0E-09
1.0E-08
1.5E-08
2.0E-08
2.5E-08
3.0E-08
3.5E-08
4.0E-08
4.5E-08
5.0E-08
606 608 610 612 614 616 618 620 622
Wavelength / nm
Ab
so
rpti
on
Co
eff
icie
nt
/ c
m-1
Measured
HITRAN '06
Lab observations in the visible (broad band CRDS)
For dimer spectroscopy
Need accurate description of monomer contribution
Including weak lines
A.J.L. Shillings, S.M. Ball, M.J. Barber, J. Tennyson & R.L. Jones, Atmos. Chem. Phys. (to be submitted)
Comparison between UCL09 and HITRAN08
0.6
0.7
0.8
0.9
1
1.1
1.2
1.3
1.4
1.5
1.6
6000 6500 7000 7500 8000 8500 9000 9500 10000 10500 11000
Frequency / cm-1
Ra
tio o
f UC
L0
9/H
ITR
AN
08
Anomaly in HITRAN data from 8000 to 9500 cm-1
Vibrational band intensities
• Calculate from (perturbed) monomer vibrational wavefunctions• Requires Eckart embedding of axis frame• Use HBB 12 D dipole moment surface (DMS) corrected with
accurate monomer DMS CVR: L. Lodi et al, J Chem Phys., 128, 044304 (2008)
Issues:• PES used to generate monomer wavefunctions• (Cut) through 12 D DMS used
1500 2500 3500 4500 5500 6500 7500 8500 9500 10500 11500
1.00E-028
1.00E-026
1.00E-024
1.00E-022
1.00E-020
1.00E-018
1.00E-016
Donor (equilibr ium)
A c c eptor(equilibr ium)
Monomer
1500 2500 3500 4500 5500 6500 7500 8500 9500 10500 11500
1.00E-028
1.00E-026
1.00E-024
1.00E-022
1.00E-020
1.00E-018
1.00E-016
Donor (per turbed)
A c c eptor (per turbed)
Monomer
Estimating transition frequencies
Band centre from monomer DVR3D calculation
Blue/red shift from calculation on perturbed PES
Vibrational fine structure from dimer dimer transitions
Simulate spectra at “295 K”
• Assume 4.5% dimer concentration• Rotational band profile 30 cm-1 (too narrow?)• Predictions give absolute intensities• 6D averaging
But:
Vibrational substructure still only for low T
(8 J=0 states per symmetry)
Results preliminary (main calculations in progress)
0.00E+000
1.00E-021
2.00E-021
3.00E-021
4.00E-021
5.00E-021
6.00E-021
7.00E-021
8.00E-021
9.00E-021
1.00E-020
1300 1400 1500 1600 1700 1800 1900
Frequency / cm-1
Inte
nsi
ty /
cm m
ol-1
Salmi
WD(S&K-2003)
MTCKD-1.1, 293K
RAL-2007/295K/
UCL
0.00E+000
5.00E-021
1.00E-020
1.50E-020
2.00E-020
2.50E-020
3500 3550 3600 3650 3700 3750 3800 3850 3900 3950 4000
Frequency / cm-1
Inte
nsi
ty /
cm m
ol-1
Salmi
WD(S&K-2003)
MTCKD-1.1, 293K
RAL-2007/295K/
UCL
0.00E+000
2.00E-022
4.00E-022
6.00E-022
8.00E-022
1.00E-021
1.20E-021
1.40E-021
1.60E-021
1.80E-021
2.00E-021
5000 5100 5200 5300 5400 5500 5600
Frequency / cm-1
Inte
nsi
ty /
cm m
ol-1
Salmi
WD(S&K-2003)
MTCKD-1.1, 293K
RAL-2007/295K/
UCL
0.00E+000
5.00E-023
1.00E-022
1.50E-022
2.00E-022
2.50E-022
3.00E-022
3.50E-022
4.00E-022
4.50E-022
5.00E-022
6900 7000 7100 7200 7300 7400 7500 7600
Frequency / cm-1
Inte
nsi
ty /
cm m
ol-1
Salmi
WD(S&K-2003)
MTCKD-1.1, 293K
RAL-2007/295K/
UCL
0.00E+000
1.00E-023
2.00E-023
3.00E-023
4.00E-023
5.00E-023
6.00E-023
7.00E-023
8.00E-023
9.00E-023
1.00E-022
8000 8200 8400 8600 8800 9000 9200 9400 9600 9800 10000
Frequency / cm-1
Inte
nsi
ty /
cm m
ol-1
Salmi
WD(S&K-2003)
MTCKD-1.1, 293K
RAL-2007/295K/
UCL
Further Work
• Preliminary spectra for up to 10,000 cm-1 produced.– Band profile comparisons show some encouraging
signs.– Effects of the sampling of the potential being
investigated.
• Need all states up to dissociation– Only 8 states per symmetry here– It is a challenge for a much higher number of states
• Improved band origins coming soon