Transcript vincn.pptx

64th OSU International Symposium on Molecular Spectroscopy
WH10
The rotational spectrum of
acrylonitrile to 1.67 THz
Zbigniew Kisiel, Lech Pszczółkowski
Institute of Physics, Polish Academy of Sciences
Brian J. Drouin, Carolyn S. Brauer, Shanshan Yu, John C. Pearson
Jet Propulsion Laboratory, California Institute of Technology,
Rotational spectroscopy of acrylonitrile:
Planar (Cs), relatively rigid molecule,
positioned in the ab inertial plane
a = 3.815(12) D
b = 0.894(68) D
review:
:
satellites:
smm+struct.:
mmw:
isotopic:
Gerry et al., J.Phys.Chem.Ref.Data A 8, 107 (1979)
Stolze+Sutter, Z.Naturforsch. 40a, 998 (1985)
Cazzoli+Kisiel, J.Mol.Spectrosc. 130, 303 (1988)
Demaison et al., J.Mol.Spectrosc. 167, 400 (1994)
Baskakov et al., J.Mol.Spectrosc. 179, 94 (1996)
Colmont et al., J.Mol.Spectrosc. 181, 330 (1997)
first astro:
Gardner+Winnewisser, Astrophys.J. . 195, L127 (1975)
isotopes+astro: Muller et al., J.Mol.Spectrosc. 251, 319 (2008)
Temperature dependence of
the acrylonitrile rotational
spectrum:
spectra measured in
this work
a type transitions
b type transitions
Spectra measured with the cascaded frequency multiplication
spectrometer at jpl:
Drouin, Mailwald, Pearson, Rev.Sci.Instr. 76, 093113 (2005)
Broadband coverage possible well into the THz region with single scans reaching
frequency spans of 100 GHz.
All spectra were merged into a single file:
1600 GHz:
n = 108 (6233)
500 GHz:
n = 30 (65)
JPL spectra/MHz
290000.00
390000.00
818379.84
850000.03
966800.00
1060000.00
1576000.00
1648000.00
Span/GHz
-- 320000.00
-- 540000.00
-- 846999.96
-- 929999.95
--1050000.00
--1160000.00
--1626000.00
--1668000.00
30
150
28.6
80
83.2
100
50
20
TOTAL = 541.8 Gb
AABS has been applied to many different types of broadband spectra:
FASSST, cascaded multiplication THz, chirped pulse FTMW, Bruker FTIR..
Good visibility of high-J,
aR-type transitions
In this Loomis-Wood type display
spectral strips are aligned on
frequencies Ka= 0 transitions for
successive values of J.
This approach allows rapid
assignment and data file
construction.
At the same time abundant
spectra rapidly produce
various surprises.
Understanding of the 1.0 THz spectrum:
The majority of the visible transitions are b-type, and the strongest
a-type transitions are indicated by 
obs.
calc.
bQ,
Ka=12←11
Understanding of the 1.6 THz spectrum:
obs.
calc.
Perturbations in the lowest vibrational states in acrylonitrile:
Notation used for identified
perturbations, in this case
between:
Ka = 18 in 11=1 and
Ka = 22 in g.s.
Principal perturbations identified in aR-type g.s. transitions:
g.s. lines
Differences relative to effective single state
fits are plotted.
Broadband coverage possible well into the THz region with single scans reaching
frequency spans of 100 GHz.
Ka = 6
Ka = 4
11 = 1 lines
Ka = 4
The Hamiltonian:
The g.s. and 11=1 both belong to the A’ representation of the Cs point group. These
states can thus be connected by Fermi resonance and c-axis Coriolis interactions.
The Hamiltonian is in 22 block form, where for the diagonal blocks we used Watson’s
Hamiltonian in both S- and A-reduction, and vibrational energy separation E in the
11=1 block.
The dominant off-diagonal contribution between g.s. and 11=1 turns out to come from
Fermi resonance :
HF(i , j) = WF + WF J P 2 + WF K Pz 2 + …,
while for the c-axis Coriolis interaction it is possible to use :
Hc(i , j) = (Gc + GcJ + GcK + …) Pc +
(Fab + FabJ + GabK + …) (Pa Pb + Pb Pa ) + …,
although only Fab proved to be determinable.
Fits and predictions were made with the SPFIT/SPCAT package of H.M.Pickett.
The fitted spectroscopic constants for g.s.  11=1 coupling:
Broadband coverage possible well into the THz region with single scans reaching
frequency spans of 100 GHz.
The progress in measurements of the g.s. :
Symbol size proportional to (nobs-ncalc)/dn
Red symbols for
(nobs-ncalc) > 3 dn
previous: 602 lines, sfit = 94 kHz
this work: 3145 lines, sfit = 143 kHz
g.s. lines can also be affected
by very specific perturbations:
Example here shows successive g.s.
aR-type doublets for K = 12.
a
The two components should in all
cases be degenerate, but one is shifted
by perturbation with Ka = 2 of 11=1.
The effect is accounted for in the fit,
and note that the perturbation is for
Ka =10 !
Nominal interstate transitions involving the g.s.:
levels of the g.s.
{ KK == 16
10 levels of  =1
Transitions are the result of strong mixing between
a
But the mixing is at J =102 and it is necessary measure the
spectrum at 960 GHz !
Current work leads to
To compare with
a
11
E = 228.29991(2) cm-1 from the rotational spectrum
E = 228.82(18) cm-1 from the gas-phase fir spectrum
(Cole+Green, J.Mol.Spectrosc. 48,246(1973).
Comparison of some observables with calculation:
a – calculated using the 6-31G(d,p)
basis, GAMESS and VIBCA .
SUMMARY:
 Extensive measurements of the rotational spectrum of acrylonitrile have been
made, at frequencies up to 1.67 THz, and covering a total of more than 540 GHz.
 The data set for the ground state has been extended by a factor of 5 in the number
of measured lines. Coverage of quantum number values is now up to J = 129 and
Ka = 30.
 Multiple perturbations affecting ground state lines were identified and
successfully fitted in terms of coupling with 11=1, even though that state differs
in vibrational energy by 228.29991(2) cm-1 (determined in this work).
 The most spectacular perturbations are at J >100 and THz frequencies.
 New results for all 13C and for the 15N species have also been obtained.
 A ladder of perturbations extending from the ground state upwards has been
identified, and it is possible that precise energies of all low lying vibrational states
may eventually be determinable from a global analysis of the rotational spectrum.