Hyperfine splittings in the near-infrared spectrum of 14NH3

Sub-Doppler, saturation dip, measurements of transitions in the $\nu_1 + \nu_3$ band of $^{14}$NH$_3$ have been made by frequency comb-referenced diode laser absorption spectroscopy. The observed spectra exhibit either resolved or partially-resolved hyperfine splittings that are primarily determined by the $^{14}$N quadrupole coupling in the molecule. Modeling of the line shapes based on the known hyperfine level structure of the ground state of the molecule shows that, in nearly all cases, the upper state level has splittings similar to that of the same rotational level in the ground state. The data provide accurate frequencies for the line positions and the observed hyperfine splittings can be used to make or confirm rotational assignments. Of all the measurements, one transition, $^{p}$P(5,4)$_a$ at 195 994.73457 GHz, exhibits hyperfine structure which does not conform to that expected based on extrapolation from the known lower state hyperfine splittings. Examination of the known vibration-rotation level structure near the upper state energy shows that there exists a near degeneracy between this level and one in the $\nu_1 + 2\nu_4$ manifold which is of the appropriate symmetry to be mixed by magnetic hyperfine terms that couple ortho- and para- modifications of the molecule. It is possible that the unusual hyperfine splittings are a consequence of ortho-paro mixing, which has been predicted, but not previously seen in ammonia and further experimental measurements to investigate this possibility are ongoing. \textbf{Acknowledgments:} Work at Brookhaven National Laboratory was carried out under Contract No. DE-SC0012704 with the U.S. Department of Energy, Office of Science, and supported by its Division of Chemical Sciences, Geosciences and Biosciences within the Office of Basic Energy Sciences.Work at Brookhaven National Laboratory was carried out under Contract No. DE-SC0012704 with the U.S. Department of Energy, Office of Science, and supported by its Division of Chemical Sciences, Geosciences and Biosciences within the Office of Basic Energy Science

Spectral Assignments And Analysis Of The Ground State Of Nitromethane In High-resolution Ftir Synchrotron Spectra

The Fourier Transform infrared spectra of CH$_{3}$NO$_{2}$, have been recorded, in the 400-950 \wn spectral region, at a resolution of 0.00096 \wn, using the Far-Infrared Beamline at Canadian Light Source. The observed spectra contain four fundamental vibrations: the NO$_{2}$ in-plane rock (475.2 \wn), the NO$_{2}$ out-of-plane rock (604.9 \wn), the NO$_{2}$ symmetric bend (657.1 \wn), and the CN-stretch (917.2 \wn). For the lowest torsional state of CN-stretch and NO$_{2}$ in-plane rock, transitions involving quantum numbers, {\it$m''$} = 0; {\it$J''$} {$\leq$ $50$} and {\it$K$}${_a}$$^{''}$ {$\leq$ $10$}, have been assigned with the aid of an automated ground state combination difference program together with a traditional Loomis Wood approach\footnote{C.~F.~Neese., \textit{An Interactive Loomis-Wood Package, V2.0,} {\textbf{56$^{th}$}},OSU Interanational Symposium on Molecular Spectroscopy (2001).}. Ground state combination differences derived from more than 2100 infrared transitions have been fit with the six-fold torsion-rotation program developed by Ilyushin et.al\footnote{V.~V.~Ilyushin, Z.~Kisiel, L.~Pszczolkowski, H.~Mader, and J.~T.~Hougen, \textit{J.~Mol.~Spectrosc.} \underline{\textbf{259}},~26, (2010).}. Additional sextic and octic centrifugal distortion parameters are derived for the ground vibrational state

DETECTION OF TRACE AMOUNT OF WATER IN VOLATILE ORGANIC COMPOUNDS BY A K-BAND MOLECULAR ROTATIONAL RESONANCE SPECTROSCOPY

Trace amount of water has been detected in ethanol (CH$_{3}$CH$_{2}$OH) and methanol (CH$_{3}$OH) using a K-Band BrightSpec Microwave Rotational Resonance (MRR) spectrometer in the 18-26 GHz frequency range. The design of this instrument is based on segmented Chirped Pulse Fourier Transform microwave wave (CP-FTMW) spectroscopy, which exploits recent advances in digital electronics to allow fast measurement of broadband rotational spectra of polar molecules. The analysis of the observed rotational spectra reveals the presence of a weak rotational line shape of water due to sensitivity of MRR to polar volatile organic compounds . The capability for K-band MRR to extract water in a such chemical environment has been further examined and validated by spiking samples with known small amount of water. The resulting linear curves allowed the determination of limit of detections at ppm level. These findings suggest that K-band MRR has potential to be useful as a spectroscopic tool for fast detection of water in volatile organic compounds or other raw materials

FREQUENCY-COMB REFERENCED SPECTROSCOPY OF _4 AND _5 HOT BANDS IN THE _1+_3 COMBINATION BAND OF C2H2

Doppler-free transition frequencies for nub{4} and nub{5} hot bands in the band of C$_{2}$H$_{2}$ have been measured using saturation dip spectroscopy with an extended cavity diode laser referenced to a frequency comb. The frequency accuracy of the measured transitions, as judged from line shape model fits and the spectrometer stability, is better than 30 kHz. This is some 2-3 orders of magnitude improvement on the accuracy and precision of previous measurements of the line positions derived from the analysis of high-resolution Fourier transform infrared absorption spectra. The data were analyzed by determining the upper state energies, using known lower state level positions, and fitting them to a $J(J+1)$ polynomial expansion to identify perturbations. The results reveal that the upper rotational energy level structure is mostly regular but suffers $J-$localized perturbations causing level shifts between one and several hundred MHz. These perturbations are due to accidental near degeneracies with energy levels of the same $J$ and larger bending vibrational excitation. textbf{Acknowledgements}: We are most grateful to Prof. D.S Perry (U. of Akron) and Prof. M. Herman (U. Libre de Bruxelles) for providing us with detailed results from their work and helpful discussions. Work at Brookhaven National Laboratory is funded by the Division of Chemical Sciences, Geosciences and Biosciences within the Offices of Basic Energy Sciences, Office of Sciences, U.S. Department of Energy under Contract Nos. DE-AC02-98CH10886 and DE-SC0012704

SPECTROSCOPIC CHARACTERIZATION OF SMALL POLAR IMPURITIES IN GASOLINE

Small polar compounds in gasoline have been identified using a BrightSpec Fourier Transform Microwave Rotational Resonance (FT-MRR) spectrometer in the 260-290 GHz band with Headspace Sampling Module. The design of this spectrometer is based on segmented Chirped Pulse Fourier Transform millimeter wave (CP-FTmmW) spectroscopy, which exploits recent advances in digital electronics to allow the measurement of broadband rotational spectra in a few minutes. As part of efforts to determine applications for rotational spectroscopy to petrochemical problems, FT-MRR has been employed to record rotationally resolved spectra of small polar compounds in gasoline. Preliminary analysis of the observed features using the BrightSpec spectral database reveals a rich, but interpretable, pattern, due to the sensitivity of FT-MRR to only polar compounds. The complex hydrocarbon matrix, which in many analytical instruments obscures the signals from low concentration impurities, is nearly invisible in FT-MRR. Spectroscopic and quantitative analyses of detected polar compounds are underway and will be given in this talk

SPECTROSCOPIC CHARACTERIZATION OF SMALL POLAR IMPURITIES IN GASOLINE

Small polar compounds in gasoline have been identified using a BrightSpec Fourier Transform Microwave Rotational Resonance (FT-MRR) spectrometer in the 260-290 GHz band with Headspace Sampling Module. The design of this spectrometer is based on segmented Chirped Pulse Fourier Transform millimeter wave (CP-FTmmW) spectroscopy, which exploits recent advances in digital electronics to allow the measurement of broadband rotational spectra in a few minutes. As part of efforts to determine applications for rotational spectroscopy to petrochemical problems, FT-MRR has been employed to record rotationally resolved spectra of small polar compounds in gasoline. Preliminary analysis of the observed features using the BrightSpec spectral database reveals a rich, but interpretable, pattern, due to the sensitivity of FT-MRR to only polar compounds. The complex hydrocarbon matrix, which in many analytical instruments obscures the signals from low concentration impurities, is nearly invisible in FT-MRR. Spectroscopic and quantitative analyses of detected polar compounds are underway and will be given in this talk

COHERENCE-CONVERTED POPULATION TRANSFER FTMW-IR DOUBLE RESONANCE SPECTROSCOPY OF CH3OD IN THE C-H STRETCH REGION

Author Institution: Department of Chemistry, The University of Akron, Akron OH 44325; Department of Chemistry, University of Virginia, McCormick Rd., Charlottesville, VA 22904Coherence-converted population transfer microwave-infrared double resonance spectroscopy is employed to record the rotationally state-selected infrared spectra of jet-cooled CH$_3$OD in the C-H stretch region (2750$-$3020 cm$^{-1}$). The observed infrared spectra result from the E-species microwave transitions (1$_0$ \leftarrow 1$_{-1}$ at 18.957 GHz, 2$_0$ \leftarrow 2$_{-1}$ at 18.991 GHz, and 3$_0$ \leftarrow 3$_{-1}$ at 19.005 GHz). The present spectra of CH$_3$OD contain 17 interacting vibrational bands ($J^{\prime}$ = 0). In additional to the three C-H stretch fundamentals ($\nu_3$:2841.7 cm$^{-1}$, $\nu_9:2954.4 cm$^{-1}$and$\nu_2:2998.9 cm$^{-1}$), 14 additional band origins are found in the region of the binary combinations of the CH bends (2890$-$2950 cm$^{-1}$). Although the A-species was inaccessible in the present work, the pattern of E-species reduced energies suggests that the torsional tunneling splittings of $\nu_3$ and $\nu_9$ are normal, whereas $\nu_2$ is inverted. The number and distribution of the observed vibrational bands support a stepwise coupling scheme in which the CH stretch bright state couples first to the binary C-H bend combinations, and then to all of the higher order vibrational combinations. A time-dependent interpretation in the asymmetric region indicates a fast (170 fs) initial decay of the bright state