1. Lowest vibrational states of acrylonitrile
70th International Symposium on Molecular Spectroscopy TB02
Lowest vibrational states of acrylonitrile
Zbigniew Kisiel,
Institute of Physics, Polish Academy of Sciences, Warszawa, Poland
Marie-Aline Martin-Drumel,
Spectroscopy Lab, Harvard-Smithsonian Center for Astrophysics,
Cambridge MA, USA
Olivier Pirali
AILES beamline, Synchrotron SOLEIL, Saint Aubin, France

2. Rotational and vibrational spectroscopy of acrylonitrile:
Praha2008
Rotational and vibrational spectroscopy of acrylonitrile:
Planar (Cs), relatively rigid molecule,
positioned in the ab inertial plane
a = 3.821(3) D
b = 0.687(8) D
Class 2 astrophysical weed as of 2006 !
The most recent studies by rotational spectroscopy:
gs to 211: Kisiel et al., J.Mol.Spectrosc. 280, 134 (2012)
Higher states: Lopez et al., Astronomy & Astrophysics, 572,A44(2014)
The most relevant infrared studies:
normal modes: Halverson et al., J.Chem.Phys. 16, 808 (1948)
rot. resolved: Cole + Green, J.Mol.Spectrosc. 48, 246 (1973)

3. How reliable ? Vibrational states of vinyl cyanide up to 1000 cm-1
Praha2008
Vibrational states of vinyl cyanide up to 1000 cm-1
All states marked in red have been studied by rotational spectroscopy
Rectangles identify polyads of vibrational states treated in terms of coupled fits.
Analysis of rotational perturbations resulted in:
v11 = (2) cm-1
v15 = (2) cm-1
2v11 = (2) cm-1
How reliable ?

4. The spectrometer: AILES beamline at the SOLEIL synchrotron
(Advanced Infrared Line Exploited for Spectroscopy)
Praha2008
Bruker IFS125
resolution=
0.001 cm-1
150m path
White cel
0.1 mbar
242 coadded
interferograms

5. The recorded spectrum:
Praha2008
The recorded spectrum:
nominally cm-1
usable cm-1
water lines + baseline removed with AABS
filter cutoff

6. Vibrational transitions:
Praha2008
Vibrational transitions:
4 fundamentals (v11, v15, v10, v14)
5 hot bands
1 overtone (2v15)
c-type
b-type
Analysis was carried out with SPFIT/SPCAT using AABS as the graphical front end.
The global fit involves 11 vibrational states and uses a practically unmodified Coriolis+Fermi interaction model from previous works.

7. The b-type 11 fundamental and its first hot-band:
Praha2008
The b-type 11 fundamental and its first hot-band:
180
200
220
Cole + Green, J.Mol.Spectrosc. 48, 246 (1973)

8. The c-type 15 fundamental and hot band:
Praha2008
18O: %
17O: %
H216O, v2: 1654 cm-1

9. Pure rotation:
Praha2008
Loomis-Wood plot showing high-Ka sequences of aR0,1 transitions in the ground state.
The plot was made with AABS Ka

10. The data set: ir: 0.001 cm-1 MW: MHz Edited output from PIFORM
Praha2008
ir: cm-1
MW: MHz
Edited output from PIFORM
pure rotation
fundam.
hot band
overtone

11. Data set composition: infrared microwave o-c >3 df Pure rotation:
Praha2008
Pure rotation:
Vibration-rotation:
infrared
microwave
o-c >3 df

12. Vibrational term values:
Praha2008
Vibrational term values:
from microwave perturbations only
Global fit with infrared data
CCSD(T)/

13. Anharmonicity coefficients (cm-1):
Praha2008
A similar infrared+microwave global fit for S(CN)2 also showed that relatively modest anharmonic calculations gave better xij than more extended ones. Kisiel at al., J.Phys.Chem.A 117,13815 (2013)

14. The weak a-type 10 fundamental:
Praha2008
The weak a-type 10 fundamental:
Uncertainty about the v10 assignment eliminated by direct observation+fit and anharmonic calculations ( v and Bv-B0 )
fitted data points

15. Praha2008
SUMMARY:
High-resolution cm-1 spectrum of acrylonitrile was recorded at the SOLEIL synchrotron
Vibration-rotation transitions in 10 different vibrational bands were assigned
Close to 9000 infrared transitions were combined with over transitions measured with microwave techniques into a single global fit, which encompasses perturbations in the:
g.s.  n11  n15  2n11 tetrad
n10  n11,n15 dyad
2n15  n14  3n11 triad
n10 n11  2n11,n15 dyad
Precise vibrational term values have been determined for all states up to 700 cm-1 (all states up to 800 cm-1 possible if the relatively strong v10v11 is measured, and the plentiful data shows the need for coupling terms between the polyads)
To appear in the J.Mol.Spectrosc. Special Issue on Spectroscopy with Synchrotron Radiation