Theoretical work on the water monomer and dimer Matt Barber Jonathan Tennyson University College...
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Transcript of Theoretical work on the water monomer and dimer Matt Barber Jonathan Tennyson University College...
Theoretical work on thewater monomer and dimer
Matt BarberJonathan TennysonUniversity College London
September 2009
Monomer line list
Extended to cover 800-20000 cm-1
Now uses HITRAN 2008 The HITRAN 2008 molecular spectroscopic database
Rothman, LS; Gordon, IE; Barbe, A, et al.JQSRT 110/9-10 pp533-572, 2009
Includes calculated line profile data
IUPAC group: Recommends not using Voigt profiles – introduce speed-dependent widths
Band intensities
Look at purely vibrational structure, ignoring rotation.
Can be calculated from line lists HITRAN, BT2, etc.
Model using dipole and potential surface. Calculate by allowing “forbidden” J=0 to 0
transition. Effects of dimer structure for changes in
intensities and shifts of band origins.
Experimental Band intensities
Need to go back to HITRAN 92 Not a particularly useful model Superceded by rovibrational modelling
However, can be calculated from newer databases
Makes a useful benchmark for ab initio models
Ab initio calculations
DVR software suite Go back to 1992 version for DIPJ0 program Requires transformation to Eckart co-ordinates
Start with monomer
Potential energy surface Spectroscopically determined potential energy surfaces of the (H2O)-O-16, (H2O)-O-
17, and (H2O)-O-18 isotopologues of water Shirin, SV; Polyansky, OL; Zobov, NF, et al.JOURNAL OF MOLECULAR SPECTROSCOPY 236/2, 2006
CVR Dipole surface A new ab initio ground-state dipole moment surface for the water molecule, Lodi, L;
Tolchenov, RN; Tennyson, J, et al.JOURNAL OF CHEMICAL PHYSICS 128/4, 2008
Integrated and calculated bands compared
1E-25
1E-24
1E-23
1E-22
1E-21
1E-20
1E-19
1E-18
1E-17
1E-16
0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
Frequency / cm-1
Inte
nsi
ty /
HIT
RA
N u
nit
s
DVR HITRAN
Moving to the Dimer
New dimer dipole surface
One molecule in ground state, the other in excited state
Large r (100 a.u.) to compare with monomer
Apply correction from monomer
Move to equilibrium configuration (and others in due course)
Uncorrected band intensities
1E-26
1E-25
1E-24
1E-23
1E-22
1E-21
1E-20
1E-19
1E-18
1E-17
1E-16
0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
Frequency / cm-1
Inte
nsi
ty /
HIT
RA
N u
nit
s (c
m m
ol-1
)
Monomer Acceptor(large-r) Donor (large-r)
Corrected Band Intensities at large r
1E-26
1E-25
1E-24
1E-23
1E-22
1E-21
1E-20
1E-19
1E-18
1E-17
1E-16
0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
Frequency / cm-1
Inte
nsi
ty /
HIT
RA
N u
nit
s (c
m m
ol-1
)
Monomer Acceptor(large-r, corrected) Donor(large-r,corrected)
Corrected Band Intensities
1E-26
1E-25
1E-24
1E-23
1E-22
1E-21
1E-20
1E-19
1E-18
1E-17
1E-16
0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
Frequency / cm-1
Inte
nsi
ty /
HIT
RA
N u
nit
s (c
m m
ol-1
)
Monomer Acceptor(corrected) Donor (corrected)
Band intensities to spectra
Band origins From Ross’s work
Band profiles Good approximation at low T More work needed at room temperature
What resolution is required?
Water dimer spectrum (preliminary)
1.00E-24
1.00E-23
1.00E-22
1.00E-21
1.00E-20
1.00E-19
1.00E-18
1000.00 1500.00 2000.00 2500.00 3000.00 3500.00 4000.00 4500.00 5000.00 5500.00 6000.00
Frequency / cm-1
Inte
nsi
ty /
HIT
RA
N u
nit
s