Transcript vincnv4.pptx

67th OSU International Symposium on Molecular Spectroscopy
TH10
Perturbations and vibrational energies in
acrylonitrile from global analysis of its
mm-wave to THz rotational spectrum
Zbigniew Kisiel,a Lech Pszczółkowski,a
Brian J.Drouin,b Carolyn S.Brauer,b Shanshan Yu,b John C.Pearson,b
Ivan R.Medvedev,c Sarah Fortman,d Christopher Neesed
aInstitute
bJet
of Physics, Polish Academy of Sciences, Warszawa, Poland
Propulsion Laboratory, California Institute of Technology,
4800 Oak Grove Drive, Pasadena, CA 91109-8099
cDepartment
dDepartment
of Physics, Wright State University, Dayton, OH 45435
of Physics, The Ohio State University, Columbus, OH 43210
Our previous work on THz-level spectrum of acrylonitrile:
J.Mol.Spectrosc. 2009:
g.s.  n11 perturbations
J.Mol.Struct. 2011:
g.s.  n11 perturbations in
isotopic acrylonitrile
MH09, OSU Symposium 2011
g.s.  n11  n15 fit
n10  n11n15 fit
The recorded spectra:
Multiplier of cmw-region pump frequency in cascaded multiplication
Analysis: AABS package
 Spectrum handling: single spectrum (36Mpoints @ 0.05 MHz) + modified
baseline subtraction
 Loomis-Wood displays: assignment
 Difference-frequency plots: location of pairwise perturbations
 Distribution plots: essential book-keeping for large data sets
AABS =
Assignment and Analysis of Broadband Spectra,
available at: http://info.ifpan.edu.pl/~kisiel/prospe.htm
Improved baseline subtraction
in AABS:
Raw spectrum
a) Standard subtraction: baseline
determined by least-squares smoothing
with a long window (red bar)
J.Mol.Spectrosc. 158, 318 (1993)
b) Narrower smoothing window leads to
artefacts near very strong lines
c) Blanking of strongest lines prior to
baseline derivation allows using
shorter smoothing windows
Interactions and Hamiltonian:
Cs symmetry point group:
A’  A’ = A’
c-axis Coriolis + Fermi
A’  A’’ = A’’
a-axis + b-axis Coriolis
g.s.
c+F
n11
0
0
a+b
c+F
n15
a+b
2n11
Some resonances are visible without special techniques:
Matching missing segments at
J=55,56 in bQ-type bands in n11
and n15 states
More detailed insight is possible with resonance plots:
Scaled frequencydifference plots
aR-type
transitions
n11  n15 resonance
a-axis and b-axis
Coriolis
 530 GHz
n11  2n11 resonance
c-axis Coriolis
and Fermi
 865 GHz
Perturbation induced
interstate transitions:
Two pairs of strongly mixed
states resulting in many
different Q- and R-type
interstate transitions
533 to 1800 GHz
Examples of the fourth type of pairwise resonance:
n15  2n11 resonance
a-axis and b-axis
Coriolis
 460 GHz
 860 GHz
Mopping up operations allowed by the final fit:
n11  2n11 resonance
c-axis Coriolis
and Fermi
(with Ka=3 levels in 2n11)
 880 GHz
g.s.  n11 resonance
c-axis Coriolis
and Fermi
 985 GHz
Mixing coefficient plot:
Plots of (1-Pmix) for energy levels allow spotting resonances by connecting similarly shaped islands of
perturbations in the horizontal (that is the J) direction
Key results from the four-state fit of g.s. + n11 + n15 + 2n11:
Fitted
lines
g.s.
n11
n15
2n11
TOTAL
4990
3395
2701
2183
Rejected
@10s
0
0
26
16
Deviation
/MHz
Deviation
rms
0.144
0.157
0.191
0.241
0.713
0.781
0.989
1.256
12769
 Parameters of fit:
DE
/cm-1
228.29986(2)
332.67811(2)
457.17496(2)
0.905
decadic level rotational Hamiltonian for each state
+ only 20 interstate coupling terms
+ 3 energy differences
 Advance in numbers of fitted lines for g.s.+ n11:
4990+3395 now
3145+1989 in JMS2009
 All n11 lines now in fit while 91 of those lines were rejected by the JMS2009 fit
Data set distribution plot:
Quick overview of quantum
number and transition type
coverage in the data set
Colour marks obs-calc values
greater than 3s, different colours
for +ve and –ve deviations
SUMMARY:
 The coverage of the room temperature rotational spectrum of acrylonitrile has
been increased in extent to a total of 1170 GHz corresponding to 61.6% of the
range up to the upper frequency limit to 1.9 THz
 Continuous record of the 182-640 GHz segment
 Broadband coverage turned out to be crucial to locating specific pairwise
perturbations involving the four lowest vibrational states
 Global fit of data for the gs + n11 + n15 + 2n11 now encompasses 12769
measured transitions at rms deviation of close to unity
 The precise values of vibrational energies (determined entirely from rotational
perturbations), x11,11, and Bv-B0 allow interesting comparisons and calibration of
ab initio anharmonic force field calculations: see the broadband issue of
J.Mol.Spectrosc.
 Coupled fits of the n10  n11,n15 dyad and of the 2n15  n14  3n11 triad have
also been successfull but connections with the other states are still to be identified
Special thanks to the Microwave
Laboratory at the OSU Department
of Physics :
for stimulating new approaches to the
analysis of broadband spectra,
for making all my visits to the OSU
Symposium possible.