1 recent caviar activities at cambridge a.j.l. shillings 1, s.m. ball 2 and r.l. jones 1 1...
Post on 22-Dec-2015
215 views
TRANSCRIPT
1
Recent CAVIAR activities at Cambridge
A.J.L. Shillings1, S.M. Ball2 and R.L. Jones1
1University of Cambridge, Department of Chemistry, Lensfield Road, Cambridge, CB1 2EW2 University of Leicester, Department of Chemistry, Leicester, LE1 7RH
2
Outline
1. BBCRDS Instrumental modifications• Previous iteration of design gave access to v.high temperatures (150C), but
introduced T gradients and uncertainties.
2. BBCRDS Measurements and Analysis• Results using different datasets to fit the measured data
3. Infra-Red BBCEAS introduction• New system hardware
• Potential light sources
• Complexities of CEAS vs CRDS.
3
Absorption cell modifications
•‘Coolant’ = water/antifreeze mix
•Tested T range 5 – 95 C (expect larger)
•V. Small (<1C) T gradients at 90C
•Entire gas delivery system
thermostatted at cell temperature –
No cold points (avoids aerosol)
4
Fitting Results (1)
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
rba
nc
e /
cm
-1
Measured
Predicted Dimer
•44% RH at 88 C (361K) – 6.1*1018 molec cm-3
•‘Average’ K(361) = 0.16 atm-1 (6.4*10-22 molec-
1 cm3)
5
Water Results (1)
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
rba
nc
e /
cm
-1
Measured
HITRAN '06
HITRAN’06 -clearly has imperfections.
6
Water Results (1)
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
rba
nc
e /
cm
-1
Measured
UCL '08
UCL ’08 - seems to be doing a much better job.
- self and foreign broadening parameters taken from HITRAN
(either default values [Foreign 0.07cm-1atm-1, Self 0.12cm-1atm-1], or average (assigned) values over wavelength range of interest)
7
Water Results (2)
0.00E+00
2.00E-27
4.00E-27
6.00E-27
8.00E-27
1.00E-26
1.20E-26
1.40E-26
551 553 555 557 559 561 563 565 567
Wavelength / nm
Ab
sorp
tio
n C
ross
Sec
tio
n /
cm2/m
ole
cule
UCL_08
HITRAN 06
•UCL 08 data greatly improved fits and residuals in green region (Fieldwork - NO2 and I2 retrievals) compared to HITRAN 06
8
Water Results (3)
-2.00E-07
-1.00E-07
0.00E+00
1.00E-07
2.00E-07
3.00E-07
4.00E-07
5.00E-07
600 602 604 606 608 610 612 614
Wavelength / nm
Abs
orpt
ion
Coe
ffic
ient
/ c
m-1
MeasuredFitted (HITRAN)Residual
[H2O] series at 95C
9
Water Results (3)
-2.00E-07
-1.00E-07
0.00E+00
1.00E-07
2.00E-07
3.00E-07
4.00E-07
5.00E-07
600 602 604 606 608 610 612 614
Wavelength / nm
Abs
orpt
ion
Coe
ffic
ient
/ c
m-1
MeasuredFitted (HITRAN)Residual
-3.00E-08
-1.00E-08
1.00E-08
3.00E-08
5.00E-08
7.00E-08
600 602 604 606 608 610 612 614
Wavelength / nm
Ab
sorp
tion
Co
eff
icie
nt
/ cm
-1
Residual
Lorentzian Fit
0.0E+00
1.0E-07
2.0E-07
3.0E-07
4.0E-07
5.0E-07
6.0E-07
0.E+00 2.E+18 4.E+18 6.E+18 8.E+18
[Water] / molecules/cm3L
ore
ntz
Sca
lin
g F
acto
r
10
Water Results (3)
-2.00E-07
-1.00E-07
0.00E+00
1.00E-07
2.00E-07
3.00E-07
4.00E-07
5.00E-07
600 602 604 606 608 610 612 614
Wavelength / nm
Ab
so
rpti
on
Co
eff
icie
nt
/ c
m-1
MeasuredFitted (UCL)Residual
11
Water Dimer Results (3)
-2.00E-07
-1.00E-07
0.00E+00
1.00E-07
2.00E-07
3.00E-07
4.00E-07
5.00E-07
600 602 604 606 608 610 612 614
Wavelength / nm
Ab
so
rpti
on
Co
eff
icie
nt
/ c
m-1
MeasuredFitted (UCL)Residual
-5.00E-08
-3.00E-08
-1.00E-08
1.00E-08
3.00E-08
5.00E-08
7.00E-08
9.00E-08
1.10E-07
1.30E-07
600 602 604 606 608 610 612 614
Wavelength / nm
Ab
so
rpti
on
Co
eff
icie
nt
/ c
m-1
Residual
y = 0.9898x
0.00E+00
1.00E+18
2.00E+18
3.00E+18
4.00E+18
5.00E+18
6.00E+18
7.00E+18
0.00E+00 1.00E+18 2.00E+18 3.00E+18 4.00E+18 5.00E+18 6.00E+18 7.00E+18
BBCRDS [H2O] / moleclues /cm3
Hy
gro
m. [
H2O
]/ m
ole
clu
es
/cm
3
14
IR BBCEAS
•Hardware
•Princeton Instruments Spectra-Pro SP-2300i spectrograph
•Princeton Instruments OMA-V InGaAs linear photodiode array (1024 pixels). Spectral coverage 2.2 – ~1.0 μm. (Liquid nitrogen cooled).
•In situ - currently writing control and acquisition software.
15
IR BBCEAS
Light Sources
•Supercontinuum fibre-optic laser (Fianium SC400)
•High Power, excellent coherence (good for coupling light into a cavity), but long term stability (intensity and spectral) to be quantified
•High Power LED
•Group has extensive experience with LEDs, can be driven at high frequency (phase-shifting potential), cheap but relatively low power (S/N issues?)
•Xenon arc lamps
•High power but potential instability.
16
IR BBCEAS
CEAS not inherently calibrated (unlike CRDS) – need a method to determine mirror reflectivity
Possibilities:
•Phase shifting
•Introduce known absorber
•e.g. (O2)2
•calibrated cylinder of an organic?
d
R
I
Io )(1.1(
)(
1
)(
11(
occ.f.
tan
17
Conclusions
•Fitting challenging owing to uncertainties in databases.
•UCL dataset seems to be doing a better job than HITRAN.
•Attempt to develop fitting methods that don’t rely on databases. (fitting low [H2O] to high [H2O])
•Complete setup of IR system
•Trial light sources
•Determine most suitable method to derive R(λ)
Next Steps