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 Neese d a Institute of Physics, Polish Academy of Sciences, Warszawa, Poland b Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA c Department of Physics, Wright State University, Dayton, OH d Department of Physics, The Ohio State University, Columbus, OH th OSU International Symposium on Molecular Spectroscopy TH10

Our previous work on THz-level spectrum of acrylonitrile: J.Mol.Spectrosc. 2009: g.s.  11 perturbations J.Mol.Struct. 2011: g.s.  11 perturbations in isotopic acrylonitrile MH09, OSU Symposium 2011 g.s.  11  15 fit 10  fit 10  fit

The recorded spectra: Multiplier of cmw-region pump frequency in cascaded multiplication

Analysis: AABS package  Spectrum handling: single spectrum 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 = A ssignment and A nalysis of B roadband S pectra, available at:

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: C s symmetry point group: A’  A’ = A’ c-axis Coriolis + Fermi A’  A’’ = A’’ a-axis + b-axis Coriolis g.s. c+F a+b c+F a+b

Some resonances are visible without special techniques: Matching missing segments at J=55,56 in b Q-type bands in 11 and 15 states

More detailed insight is possible with resonance plots: Scaled frequency- difference plots a R-type transitions 11  2 11 resonance c-axis Coriolis and Fermi  865 GHz 11  15 resonance a-axis and b-axis Coriolis  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: 15  2 11 resonance a-axis and b-axis Coriolis  460 GHz  860 GHz

Mopping up operations allowed by the final fit: g.s.  11 resonance c-axis Coriolis and Fermi  985 GHz 11  2 11 resonance c-axis Coriolis and Fermi (with K a =3 levels in 2 11 )  880 GHz

Mixing coefficient plot: Plots of (1-P mix ) 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  11 : Fitted Rejected DeviationDeviationDE  /MHzrms/cm-1 g.s (2) (2) (2) TOTAL  Parameters of fit: decadic level rotational Hamiltonian for each state + only 20 interstate coupling terms + 3 energy differences  11  Advance in numbers of fitted lines for g.s. +  11 : now in JMS  All 11 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 3 , 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 GHz segment  Broadband coverage turned out to be crucial to locating specific pairwise perturbations involving the four lowest vibrational states gs  Global fit of data for the gs now encompasses measured transitions at rms deviation of close to unity  The precise values of vibrational energies (determined entirely from rotational perturbations), x 11,11, and B v - B 0 allow interesting comparisons and calibration of ab initio anharmonic force field calculations: see the broadband issue of J.Mol.Spectrosc. 10   14  3 11  Coupled fits of the 10  11, 15 dyad and of the 2 15  14  3 11 triad have also been successfull but connections with the other states are still to be identifiedSUMMARY:

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.