Transcript Ohio_Vortrag.ppt

High-Resolution Spectroscopy on
Doubly Deuterated Ammonia
up to 2.6 THz
61st International Symposium on
Molecular Spectroscopy,
Ohio State University
Christian Endres
Overview
• Motivation
• Spectrometer Setup
• Measurements on ND2H
• Conclusion
Ohio, International Symposium on Molecular Spectroscopy
22.6.2006
Christian Endres
Motivation
Astrophysical Relevance
Deuterium fractionation has become an important topic in dark clouds
Cosmic abundance: D/H ~ 1.4 x 10-5, but
NH2D / NH3 ~ 0.1
ND2H / NH2D ~ 0.05
ND3 / ND2H ~ 0.02
First interstellar detections of the ammonia isotopic species:
NH3: 1968
NH2D: 1978
ND2H: 2000
ND3: 2002
Light hydrides such as ammonia and its isotopic species have strong
transitions in the THz region
Ohio, International Symposium on Molecular Spectroscopy
22.6.2006
Christian Endres
Motivation
New Telescopes for the THz-region:
CONDOR / APEX
Atacama Pathfinder Experiment
1.3 -1.5 THz
First Light Oct. 2005
Stratospheric Observatory For
Infrared Astronomy
1.6 -1.9 THz and 2.4 – 2.7 THz
GREAT / SOFIA
scheduled 2008
HIFI / Herschel
Herschel Space Observatory
0.5 - 1.25 THz and 1.4 - 1.9 THz
Start Aug 2008
Ohio, International Symposium on Molecular Spectroscopy
22.6.2006
Christian Endres
Motivation
Previous works
Laboratory spectroscopic investigations on ND2H:
Large dataset of microwave transitions up to 515 GHz and
quantitative description of the inversion - rotation spectra
De Lucia & Helminger, J. Mol. Spectrosc. 54 (1975) 200-214
Improvement of the Hamiltonian, analysis of both inversion substates simultaneously and determination of structural parameters
Cohen & Pickett, J. Mol. Spectrosc. 93 (1982) 83-100
Large dataset of FIR transition frequencies up to 220 cm-1 (6.6 THz)
(+ some MW lines)
Fusina et al., J. Mol. Spectrosc. 127 (1988) 240-254
Ohio, International Symposium on Molecular Spectroscopy
22.6.2006
Christian Endres
ND2H
Spectrum
Asymmetric top
 = −0.2284 (prolate)
Inversion causes splitting into
lower symmetric and upper
asymmetric substates
Each inversion doublet
consists of one ortho- and
one para- state
Weak b-type transitions
within inversion substates
(b =0.21 D)
Strong c-type transitions
between inversion substates
( c =1.47 D )
Ohio, International Symposium on Molecular Spectroscopy
22.6.2006
Christian Endres
ND2H
Spectrum
Asymmetric top
 = −0.2284 (prolate)
Inversion causes splitting into
lower symmetric and upper
asymmetric substates
Each inversion doublet
consists of one ortho- and
one para- state
Weak b-type transitions
within inversion substates
(b =0.21 D)
Strong c-type transitions
between inversion substates
( c =1.47 D )
Ohio, International Symposium on Molecular Spectroscopy
22.6.2006
Christian Endres
ND2H
Spectrum
220
221
40
211
10
0
c-type
20
212
202
b-type
E [cm-1]
30
para
ortho
Asymmetric top
 = −0.2284 (prolate)
Inversion causes splitting into
lower symmetric and upper
asymmetric substates
Each inversion doublet
consists of one ortho- and
one para- state
110
111
101
Weak b-type transitions
within inversion substates
(b =0.21 D)
000
Strong c-type transitions
between inversion substates
( c =1.47 D )
Ohio, International Symposium on Molecular Spectroscopy
22.6.2006
Christian Endres
ND2H
Spectrum
Asymmetric top
 = −0.2284 (prolate)
1
Intensity [ a.u.]
0.8
Inversion causes splitting into
lower symmetric and upper
asymmetric substates
0.6
Each inversion doublet
consists of one ortho- and
one para- state
0.4
Weak b-type transitions
within inversion substates
(b =0.21 D)
0.2
0
0
1
2
3
Frequency [THz]
Calculated stick spectrum @ 75 K
Ohio, International Symposium on Molecular Spectroscopy
4
Strong c-type transitions
between inversion substates
( c =1.47 D )
22.6.2006
Christian Endres
ND2H
Spectrum
Asymmetric top
 = −0.2284 (prolate)
1
Intensity [ a.u.]
0.8
Inversion causes splitting into
lower symmetric and upper
asymmetric substates
0.6
Each inversion doublet
consists of one ortho- and
one para- state
0.4
Weak b-type transitions
within inversion substates
(b =0.21 D)
0.2
0
0
1
2
3
Frequency [THz]
Calculated stick spectrum @ 75 K
Ohio, International Symposium on Molecular Spectroscopy
4
Strong c-type transitions
between inversion substates
( c =1.47 D )
22.6.2006
Christian Endres
ND2H
Spectrum
E [cm -1]
a)
E [cm -1]
b)
c)
Coriolis Interaction between closely
spaced states with:
J=0, Ka=0, Kc=±1, and v=1
Especially strong perturbation if
asymmetry splitting  inversional splitting,
like in case b)
E [cm -1]
Fig. :
Ohio, International Symposium on Molecular Spectroscopy
para
ortho
a) Inversion splitting > Asymmetry splitting
b) Inversion splitting  Asymmetry splitting
c) Inversion splitting < Asymmetry splitting
22.6.2006
Christian Endres
Spectrometer
in Cologne
BWO
Sideband
BWO + Superlattice Multiplier
0
0.5
1.5
1.0
2.0
2.5
3.0
Frequency [THz]
THz spectrometer (BWOs):
0.08 – 1.2 THz
Sideband spectrometer COSSTA:1.75 – 2.01 THz
Multiplier spectrometer
0.24 – 2.7 THz
Ohio, International Symposium on Molecular Spectroscopy
22.6.2006
Christian Endres
Spectrometer
New Superlattice Setup
PC
2F Modulation
Synthesizer
Synthesizer
350 MHz
Lock-In
16 GHz
PLL
IF
Harmonic
Mixer
Lense Absorption cell
Lense
SL
~250 GHz
Superlattice
Multiplier (SL)
0.75 - 2.6 THz
Bolometer
Power Supply
Ohio, International Symposium on Molecular Spectroscopy
22.6.2006
Christian Endres
ND2H
Measurements
Partly resolved HFS for low
rotational quanta J
Largest contribution due to electric
quadrupole interaction of 14N
Frequency [GHz]
Spectrum measured with the 5th harmonic of
a BWO generated by the superlattice
multiplier
Ohio, International Symposium on Molecular Spectroscopy
 El. quadrupole interaction is
considered in Ĥ and in fitting the line
profile
Line accuracy is checked by using
closed cycles of transitions
(Ritz-Combination-Principle)
22.6.2006
Christian Endres
ND2H
Measurements
Measurements from 0.078 - 2.578 THz
Frequency uncertainty:
mostly
10-100 kHz
partly
- 500 kHz (>2 THz )
240 transitions in total
(105 b-type, 135 c-type)
Frequency [THz]
Radiation of the 11th harmonic
used to measure spectra up to 2.58 THz
Ohio, International Symposium on Molecular Spectroscopy
15 transitions involving strongly
perturbed levels up to JKaKc= 138 5 ,v = 0
22.6.2006
Christian Endres
ND2H
Fit
Hamiltonian
Interaction Constants ( in MHz )
• S-reduced Hamiltonian
F
Ĥ = Ĥvv + Ĥ01 + ĤHfs
Ĥvv : terms up to 8th order
Ĥ01 : terms up to 8th order
• 54 Parameters used in the fit
Lines used in the fit
# Lines
RMS
This work
240
0.99
In total
923
0.90
3129.951(101)
FK
-9.327(34)
FJ
0.8529(40)
FKK
0.02401(85)
FJK x 103
0.383(290)
FJJ x 103
-1.521(35)
FKKK x 103
0.03216(195)
FJKK x 103
-0.02250(102)
FJJK x 106
-3.090(84)
FJJJ x 106
-0.0949(105)
Coriolis interaction between inversion substates substantially improved
Ohio, International Symposium on Molecular Spectroscopy
22.6.2006
Christian Endres
ND2H
Predictions
Frequency predictions up to 3 THz have been calculated using spcat
→ www.cdms.de
Uncertainties of our predictions
Up to J = 15 and Ka = 9
< 1 MHz
For low lying rotational states, which are
most important for astro. observations
< 100 kHz (≈10 m/s at 3 THz)
Endres et al., J.Mol.Struct., in press. 2006
Ohio, International Symposium on Molecular Spectroscopy
22.6.2006
Christian Endres
Conclusion
First successful application of the Superlattice Multiplier to record
high resolution spectra with kHz accuracy up to THz frequencies.
Reliable predictions of the inversion-rotation spectra of ND2H for
astronomical observations up to 3 THz
→ www.cdms.de
Ohio, International Symposium on Molecular Spectroscopy
22.6.2006
Christian Endres