perturbations and vibrational energies in acrylonitrile from global analysis of its mm-wave to thz...
TRANSCRIPT
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 of Physics, Polish Academy of Sciences, Warszawa, PolandbJet Propulsion Laboratory, California Institute of Technology,
4800 Oak Grove Drive, Pasadena, CA 91109-8099cDepartment of Physics, Wright State University, Dayton, OH 45435
dDepartment of Physics, The Ohio State University, Columbus, OH 43210
67th OSU International Symposium on Molecular Spectroscopy TH1067th OSU International Symposium on Molecular Spectroscopy TH10
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 subtractionin 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 0 0 n11 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 frequency-difference plots
aR-type transitions
n11 2n11 resonance
c-axis Coriolisand Fermi
865 GHz
n11 n15 resonance
a-axis and b-axisCoriolis
530 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-axisCoriolis
460 GHz
860 GHz
Mopping up operations allowed by the final fit:
g.s. n11 resonance
c-axis Coriolisand Fermi
985 GHz
n11 2n11 resonance
c-axis Coriolisand Fermi
(with Ka=3 levels in 2n11)
880 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 Rejected Deviation Deviation DElines @10s /MHz rms /cm-1
g.s. 4990 0 0.144 0.713n11 3395 0 0.157 0.781 228.29986(2)
n15 2701 26 0.191 0.989 332.67811(2)
2n11 2183 16 0.241 1.256 457.17496(2)
TOTAL 12769 0.905
Parameters of fit: 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 now3145+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
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
SUMMARY:
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.