Transcript 2009_Columbus_c2h2.ppt

Terahertz spectroscopy and global analysis
of the bending vibrations of C2H2 and C2D2
Shanshan Yu, Brian Drouin, John Pearson, Herbert Pickett
Valerio Lattanzi and Adam Walters
Yu et al., Astrophys. J. 698 (2009) 2114-2120
Yu et al., Astrophys. J. (submitted)
Vibrational modes of C2H2 and C2D2
C2H2
C 2 D2
n1
H
C
C
H
3373 cm-1
2705 cm-1
n2
H
C
C
H
1974 cm-1
1765 cm-1
n3
H
C
C
H
3295 cm-1
2439 cm-1
n4
H
C
C
H
612 cm-1
512 cm-1
n5
H
C
C
H
729 cm-1
539 cm-1
117 cm-1
(~3500 GHz)
27 cm-1
(~900 GHz)
n5 - n4
Introduction to C2H2
 12C2H2 is highly abundant in the interstellar medium
 Observed in the cold (<100K) gas with abundances from ~10-9 to 10-8 and in the
warm (100-1000K) gas with abundances up to ~10-7 to 10-6 (e.g., Evans et al.
1991; Carr et al. 1995; Lahuis and van Dishoeck 2000; Farrah et al. 2007;
Sonnentrucker et al. 2007)
 12C2H2 is present as traces in the upper atmosphere of
 Titan (Coustenis et al. 2007)
 Jupiter (Ridgway 1974)
 Uranus (Encrenaz et al. 1998)
 12C2H2 is also present as pollutant in
 The terrestrial troposphere (Kanakidou et al. 1988)
 the urban atmosphere (Goldman et al. 1981)
C2D2: a potential interstellar species
 Observed multiply deuterated interstellar molecules
 [D2CO]/[H2CO] = 0.002-0.4 (Turner 1990; Ceccarelli et al. 1998, 2001, 2002;
Loinard et al. 2000, 2001; Parise et al. 2006; Roberts and Millar 2007)
 [NHD2]/[NH3] = 0.005-0.05 (Roueff et al. 2000, 2005; Loinard et al. 2001; Gerin
et al. 2006)
 [ND3]/[NH3] = 0.0005-0.001 (Lis et al. 2002; van der Tak et al. 2002; Roueff et
al. 2005)
 [CHD2OH]/[CH3OH] =0.06-0.25 (Parise et al. 2002, 2004, 2006)
 [CD3OH]/[CH3OH] = 0.01 (Parise et al. 2004)
 [D2S]/[HDS] = 0.1 (Vastel et al. 2003)
Previous studies on C2H2 and C2D2
 Spectroscopic information on all the five vibrational modes of C2H2 and C2D2
are available
 But Spectroscopic study of 12C2H2 and
difference bands was very sparse
12C D
2 2
in the region of their n5–n4
 For 12C2H2
 only ~300 lines measured by FTIR in 52–192 cm-1 with uncertainty of 9
MHz (Kabbadj et al. 1991)
 For 12C2D2
 only 10 lines were measured with microwave precisions (Lafferty et al.
1977; Deleon and Muenter, 1987 )
 ~260 lines were measured in 30–100 cm-1 with uncertainty of 2.4 MHz
(Huhanantti et al. 1979; Huet et al. 1991 )
Experimental setup
2.8 meters
Parabolic
mirror
Si detector
Pump
Sample
Sample cell
Beamsplitter
Sample cell
Rooftop
reflector
×3
Lock-in …
PC
×2 Multiplier chain
×6
FM
RF Synthesizer
150 mTorr C2H2/C2D2 generated by passing H2O/D2O through CaC2 powder
Static quartz cells for stable molecules
3 mm thick
flat quartz window
25-35 mm
Bomco 2.75" conflat
quartz-to-metal seal
15 o
~100mm
Length = 1or 3 m
Leaking rate: 1 mTorr per week
Observed C2D2 terahertz transitions
1067920
1067950
Predicted with a logarithm of
intensity (in nm2·MHz) of -5.18
802375
802425
Predicted with logarithms of intensity (in
nm2·MHz) ranging from -6.95 to -6.37
251 12C2D2 lines observed
Observed C2H2 terahertz transitions
12C
2H 2
n5 - n4 P ff (36)
1005035 1005040 1005045 1005050 1005055 1005060 1005065 1005070
Frequency (M Hz)
Predicted with a logarithm of
intensity (in nm2·MHz ) of -6.8
20 12C2H2 lines observed
Multistate analysis of C2H2 and C2D2
V4l 4 V5l5
1100
Basis functions
Matrix elements for C2H2 and C2D2
Interactions in the bending vibrations of acetylene
1. Elements responsible for the rotational l-type resonance and doubling
2. Elements representing the vibrational l-type resonance and doubling
3. Elements accounting for the Darling-Dennison type interactions (C2D2 only)
Block form of matrix elements for C2D2
Fitting results for 12C2D2
A data set of 2092 transitions was constructed
72 parameters fitted to 1938 transitions (154 IR lines rejected)
Reduced RMS = 1.3
Microwave RMS = 0.094 MHz (261 MW data)
IR RMS = 0.00011 cm-1
Fitting results for 12C2H2
A data set of 1406 lines was constructed
34 parameters fitted to 1390 transitions
Reduced RMS = 0.5
Microwave RMS = 0.072 MHz (20 MW data)
IR RMS = 0.00016 cm-1
Acknowledgements

Tim Crawford

NASA Postdoctoral Program (ORAU)

NASA Astrophysics Research and Analysis Program (APRA)
Jet Propulsion Laboratory
California Institute of Technology
Pasadena, California
www.nasa.gov
National Aeronautics and
Space Administration