Abstracts of OSU International Symposium on Molecular Spectroscopy 2010-2013

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This collection contains the abstracts of the OSU International Symposium on Molecular Spectroscopy from 2010-2013 (and complete presentations from authors who have so authorized).

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A "WET DOG" TUNNELING MOTION AS THE CAUSE FOR THE DOUBLED ROTATIONAL SPECTRUM OF 1-IODONONAFLUOROBUTANE
(Ohio State University, 2013) Bailey, W. C.; Bohn, R. K.; Grubbs, G. S.; Kisiel, Z.; Cooke, S. A.
A chirped pulse Fourier transform microwave spectrometer has been used to record the rotational spectra of 1-iodononafluorobutane between 8 GHz and 12 GHz. The target compound was spectroscopically examined as it participated in a supersonic expansion of argon. The spectra recorded are dense owing in part to the small rotational constants, $B$ + $C$ $\approx$ 480 MHz, but also to hyperfine structure generated by the coupling of angular momenta of the iodine nucleus and the rotating molecular frame, e.g. $\mid \chi_{ab} \mid$ $\approx$ 1200 MHz. Notably all of the hyperfine components were observed as doublets. It is postulated that this doubling effect is the result of a low barrier, double minimum potential between two mirror image transoid structures. The tunneling motion between these structures resembles that of a "wet dog" shaking itself dry. Numerous transitions are shifted in frequency and it is proposed that the density of rotational energy levels from the two interacting states results in numerous perturbations to the energy levels involved. A preliminary spectral analysis of over 400 transitions will be presented, along with the results of supporting quantum mechanical calculations.
STRUCTURAL STUDIES OF PYRROLE-BENZENE COMPLEXES BY CHIRPED-PULSE ROTATIONAL SPECTROSCOPY
(Ohio State University, 2013) Lobsiger, Simon; Perez, Cristobal; Zaleski, Daniel P.; Seifert, Nathan A.; Pate, Brooks H.; Pfaffen, Chantal; Trachsel, Maria A.; Leutwyler, Samuel
Non-covalent intermolecular interactions are important in structural biology. The N-H $\cdots$ $\pi$ hydrogen bond between amino acid side chains is an important structural determinant and highly affects the secondary structure of proteins. The pyrrole-benzene complex can be viewed as a model system for studying these fundamental interactions. Previous IR and UV spectroscopic studies of the pyrrole-benzene complex by Dauster \textit{et al.} nderline{\textbf{10}}, 2827 (2008)} and Pfaffen \textit{et al.} nderline{\textbf{13}}, 14110 (2011)} support a T-shaped structure with an N-H $\cdots$ $\pi$ hydrogen bond to the benzene ring. In order to obtain accurate structural information we have investigated the broadband rotational spectrum of the supersonic-jet cooled complexes of pyrrole with benzene and benzene-\textit{d}$_{1}$ in the 2-18 GHz frequency range. In addition to the hetero dimer we have also observed the two cyclic mixed trimers (pyrrole)$_{2}$-benzene and pyrrole-(benzene)$_{2}$.
MW SYSTEMATIC STUDY OF ALKALOIDS: THE DISTORTED TROPANE OF SCOPOLINE
(Ohio State University, 2013) Ecija, Patricia; Cocinero, Emilio J.; Basterretxea, Francisco J.; Fernandez, Jose A.; Castano, Fernando; Lesarri, Alberto
Tropane alkaloids have diverse pharmacological uses and are well-known for their neurostimulant activity. Previous structure-activity-relationship established correlations between bioactivity and several aspects of ligand conformation and stereochemistry, including delicate intramolecular effects like nitrogen inversion$^{a}$. We have initiated a series of structural studies on tropane alkaloids$^{b}$, aimed to discerning their intrinsic stereochemical properties using rotational spectroscopy in supersonic jets$^{c}$. Here we extend these studies to the epoxytropanes, initially motivated to interrogate the influence of the epoxy group on nitrogen inversion and ring conformation. The rotational spectrum evidences a single structure in the gas phase, providing a first description of the (three ring) structurally-distorted tropane in scopoline. The determined rotational parameters of scopoline reveal the structural consequences of the intramolecular cyclation of scopine, which breaks the original epoxy group and creates a new ether bridge and a 7$\beta$-hydroxytropane configuration. The hydroxyl group further stabilizes the molecule by an $O-H \cdots N$ intramolecular hydrogen bond, which, in turn, forces the N-methyl group to the less stable axial form$^{b}$. The experimental work was supported by ab initio and DFT calculations.\\ $^{a}$ i) S.Singh, \emph{Chem. Rev.} 100, 925 (2000); ii) A. Krunic, D. Pan, W.J. Dunn III, S.V.S. Miariappan, \emph{Bioorg. & Med. Chem.} 17, 811 (2009).\\ $^{b}$ E.J. Cocinero, A. Lesarri, P. Ecija, J.-U. Grabow, J.A. Fernandez, F. Casta\~{n}o, \emph{Phys. Chem. Chem. Phys.} 12, 6076 (2010).\\ $^{c}$ E.J. Cocinero, A. Lesarri, P. Ecija, J.-U. Grabow, J.A. Fernandez, F. Casta\~{n}o, \emph{Phys. Chem. Chem. Phys.} 12, 12486 (2010).
GAS-PHASE STRUCTURES OF LINALOOL AND COUMARIN STUDIED BY MICROWAVE SPECTROSCOPY
(Ohio State University, 2013) Nguyen, H. V. L.; Stahl, W.; Grabow, J.-U.
The microwave spectra of two natural substances, linalool and coumarin, were recorded in the microwave range from 9 to 16 GHz and 8.5 to 10.5 GHz, respectively.Linalool is an acyclic monoterpene and the main component of lavender oil. It has a structure with many possible conformations. The geometry of the lowest energy conformer has been determined by a combination of microwave spectroscopy and quantum chemical calculations. Surprisingly, a globular rather than a prolate shape was found. This structure is probably stabilized by a $\pi$ interaction between two double bonds which are arranged in two stacked layers of atoms within the molecule. A-E splittings due to the internal rotation of one methyl group could be resolved and the barrier to internal rotation was determined to be 400.20(64) cm$^{-1}$. The standard deviation of the fit was close to experimental accuracy. For an identification of the observed conformer not only the rotational constants but also the internal rotation parameters of one of the methyl groups were needed. Coumarin is a widely used flavor in perfumery as sweet woodruff scent. The aromatic structure allows solely for one planar conformer, which was found under molecular beam conditions and compared to other molecules with similar structures. Here, the rotational spectrum could be described by a set of parameters including the rotational constants and the centrifugal distortion constants using a semi-rigid molecule Hamiltonian. Furthermore, the rotational transitions of all nine $^{13}$C isotopologues were measured in natural abundance. As a consequence, the microwave structure of coumarin could be almost completely determined.
INFRARED SPECTROSCOPY AND STRUCTURES OF MASS-SELECTED RHODIUM CARBONYL AND RHODIUM DINITROGEN CATIONS
(Ohio State University, 2013) Abbott, Heather L.; Brathwaite, Antonio D.; Duncan, Michael A.
Rhodium carbonyl cations, Rh(CO)$_{n}^{+}$, and rhodium dinitrogen cations, Rh(N$_{2})_{n}^{+}$, are produced by laser vaporization in a pulsed-nozzle molecular beam source. Mass-selected infrared photodissociation spectroscopy of these ions and their argon tagged analogs are compared to density functional theory computations. Structures of the rhodium cations are determined based upon the number, frequency position and relative intensity of the infrared active bands between 2000 and 2400 cm$^{-1}$. Computed binding energies and fragmentation patterns suggest that four carbonyl ligands bind strongly to the central rhodium cation.
THE PROTOTYPE DIPEPTIDE GLY-GLY: A ROTATIONAL STUDY
(Ohio State University, 2013) Varela, M.; Cabezas, C.; Mata, S.; Alonso, J. L.
The simplest dipeptide Gly-Gly has been examined for the first time in the gas phase by laser ablation molecular beam Fourier transform microwave (LA-MB-FTMW) spectroscopy. The nuclear quadrupole hyperfine structure of two $^{14}$N nuclei has been totally resolved allowing the conclusive identification of three conformers in the supersonic expansion. Intramolecular hydrogen bonding interactions have been analyzed on the bases of the structure of the observed conformers. Present results indicate that it is possible to face the study larger peptides using LA-MB-FTMW spectroscopy.
SLOW ELECTRON VELOCITY-MAP IMAGING OF La$_2$(C$_6$H$_6$) AND La(C$_6$H$_6$)$_2$
(Ohio State University, 2013) Silva, Ruchira; Yang, Dong-Sheng
Slow electron velocity-map imaging (SEVI) was used to study the structures and electronic states of La$_2$(C$_6$H$_6$) and La(C$_6$H$_6$)$_2$ complexes formed in a metal cluster beam source. Electron spectra obtained from SEVI have the energy resolution of $\Delta$E/eKE $\approx$ 2$\%$ at eKE=400cm$^{-1}$. The SEVI technique offers much higher data collection efficiency than pulsed-field ionization zero electron kinetic energy spectroscopy. From the SEVI spectra, adiabatic ionization energies were measured to be 32141(5) cm$^{-1}$ for La$_2$(C$_6$H$_6$) and 39033(5) cm$^{-1}$ for La(C$_6$H$_6$)$_2$. The most active vibrational transition for both complexes was identified to be a metal-ligand stretching mode with a frequency of 180 cm$^{-1}$ in the ion state. In addition, a benzene ring out-of-plane deformation mode was measured to be 303 cm$^{-1}$ for [La$_2$(C$_6$H$_6$)]$^+$ and 408 cm$^{-1}$ for [La(C$_6$H$_6$)$_2$]$^+$. By combining the spectra with theoretical calculations, we identified the $^2$A$_g$$\leftarrow$$^1$A$_g$ transition of La$_2$(C$_6$H$_6$) (C$_{2h}$) and $^3$A$\leftarrow$$^2$A of La(C$_6$H$_6$)$_2$ (C$_1$). By measuring the anisotropy parameter ($\beta$) from photoelectron angular distribution, we found that the outgoing electron was from a largely La 6s-based molecular orbital in both complexes.
UNDERSTANDING COMPLEX SPECTRAL SIGNATURES OF EMBEDDED EXCESS PROTONS IN MOLECULAR SCAFFOLDS WITH THIRD ORDER CORRECTIONS TO THE HARMONIC POTENTIAL SURFACE
(Ohio State University, 2013) Deblase, Andrew F.; Johnson, Mark A.; Lectka, Thomas; Wang, Xun; Jordan, Kenneth D.; McCoy, Anne B.
Overtones and combination bands observed in vibrational predissociation spectra of cold ions can often be anticipated by expanding the potential energy surface to third order. This is achieved by relating the third derivatives to the matrix elements that couple the allowed and forbidden states in the harmonic basis. Such a strategy has been successful in predicting Fermi resonances in formic acid clusters and some charged H-bonded complexes. Furthermore, third order couplings have been used to develop a vibrational adiabatic model in which excitation of a bright state is distributed over a Franck-Condon envelop of a lower energy mode, such as a water rocking against triatomic domains of molecular anions. Previous applications include the analysis of long vibrational progressions of soft modes in the OH stretching region of the actetate-water binary complex. Here we explore to extent to which this order of correction captures the irregular patterns associated with intramolecular proton bonds.
HIGH-RESOLUTION PHOTOELECTRON SPECTROSCOPY OF 2-BUTYNE
(Ohio State University, 2013) Jacovella, Ugo; Gans, Berenger; Merkt, Frederic
Using a coherent narrow-band vacuum-ultraviolet (VUV) laser source (bandwitdh of 0.008~cm$^{-1}$)$ \textbf{71}, 4023 (2000).}$ coupled to a photoionization and pulse-field-ionization zero-kinetic-energy photoelectron (PFI-ZEKE) spectrometer, the threshold photoionization of polyatomic molecules can be studied at high resolution. We present a new measurement of the PFI-ZEKE photoelectron spectrum of the origin band of the X$^+$~$^2$E$_{2(d)}$ $\leftarrow$~X~$^1\mathrm{A}_{1(s)}$ ionizing transition of 2-butyne at a resolution of 0.15~cm$^{-1}$. Despite this high resolution, the spectral congestion originating from the combined effects of the internal rotation, the spin-orbit coupling and the Jahn-Teller effect prevented the full resolution of the rotational structure of the photoelectron spectrum. Combined with the known structure of the X $^1$A$_{1(s)}$ ground state of 2-butyne, including the free internal rotation$ \textbf{6}, 445 (1963).}$$ \textbf{37}, 1433 (1962).}$$ \textbf{8}, 81 (1964).}$, the spectrum was used to derive information on the X$^+$~$^2$E$_{2(d)}$ ground state of the 2-butyne radical cation. The rotational branch structure of the spectrum points at a complex energy-level structure of the cation and at the importance of a shape resonance enhancing g photoelectron partial waves$ \textbf{136}, 154303 (2012).}$.
C-C BOND ACTIVATION AND COUPLING OF PROPENE INDUCED BY LA ATOM
(Ohio State University, 2013) Hewage, Dilrukshi; Tao, Hong; Silva, Ruchira; Kumari, Sudesh; Yang, Dong-Sheng
A series of La(C$_n$H$_m$) complexes with n $\leq$ 6 and m $\leq$ 12 were produced by the reactions between propene and La in a supersonic molecular beam source. Their formation and structures were investigated using mass-analyzed threshold ionization (MATI) spectroscopy in combination with theoretical calculations. Previously, we identified the formation of La(C$_3$H$_4$) and H-La(C$_3$H$_5$) through dehydrogenation and metal insertion mechanisms. In this work, we will discuss the formation of La(CH$_2$) and La(C$_4$H$_6$) by La induced C-C bond activation and coupling. La(CH$_2$) is formed by the C-C bond breakage and 1,2-hydride shift of propene and is a Schrock-type carbene complex. This complex is then coupled with the C=C bond of a second propene molecule to form La(C$_4$H$_6$) by removing two hydrogen atoms. The resultant La(C$_4$H$_6$) complex was idetified in two low-energy isomeric forms: one was a metallacycle (isomer A) and the other was lanthanum trimethylenemethane (isomer B). Both La(C$_4$H$_6$) isomers are in a doublet ground state, with isomer A in C$_s$ point group and isomer B in C$_3$$_v$. Adiabatic ionization energies and several vibrational frequencies of the two complexes were obtained from the sharp MATI spectra.
TORSION-ROTATION-VIBRATION EFFECTS IN THE $\nu_{20}$, 2$\nu_{21}$, 2$\nu_{13}$ AND $\nu_{21} + \nu_{13}$ STATES OF CH$_3$CH$_2$CN
(Ohio State University, 2013) Daly, Adam M.; Pearson, John C.; Yu, Shanshan; Drouin, Brian J.; Bermudez, C.; Alonso, J. L.
Ethyl cyanide, CH$_3$CH$_2$CN, is a highly abundant molecule in hot cores associated with massive star formation where temperatures often approach 200K. Astrophysicists would like to use the many thousands of observed lines to evaluate thermal equilibrium, temperature distributions, heating sources, and radiative pumping effects. In spite of a recent partial success in characterizing the $\nu_{20}$ and $\nu_{12}$ vibrational states~(2013) in press.}, many aspects of the spectroscopy of the $\nu_{20}$ state are not adequately characterized. Torsional splittings in the b-type spectrum of $\nu_{20}$ are typically a few MHz and many a-type transitions also show resolved torsional splittings, both are incompatible with the expected 1200 cm$^{-1}$ barrier to internal rotation in a $v_t=0$ state. Additionally all $K$ values above 2 show some obvious perturbations. The three states that lie just above $\nu_{20}$ are 2$\nu_{21}$, 2$\nu_{13}$ and $\nu_{21} + \nu_{13}$. It has been determined that $\nu_{20}$ interacts weakly with both 2$\nu_{21}$ and 2$\nu_{13}$ and that 2$\nu_{21}$ interacts weakly with 2$\nu_{13}$, in spite of their common symmetry and very close proximity. However, all the interactions of $\nu_{21} + \nu_{13}$ appear to be very strong, making assignments of the combination band particularly problematic. The numerous interactions result in wide spread anomalous torsional splittings. These splittings provide valuable insight into the nature of the interactions, however without a reasonable model, assignment of A or E to a torsional component is far from obvious. There remains no reasonable quantum mechanical description of how to proceed with a torsion-rotation-vibration analysis involving large and small amplitude motions. Regardless, everything that can be assigned in the laboratory spectrum can be securely identified in the astronomical spectrum of several sources, suggesting that a solution to this problem is needed. We present what is known and unknown in this quartet of CH$_3$CH$_2$CN states.
MASS ANALYZED THRESHOLD IONIZATION OF LUTETIUM DIMER
(Ohio State University, 2013) Wu, Lu; Roudjane, Mourad; Liu, Yang; Yang, Dong-Sheng
Lu$_2$ is produced in a pulsed laser-vaporization metal-cluster source and studied by mass-analyzed threshold ionization (MATI) spectroscopy. The MATI spectrum displays several long progressions from the transitions between various vibrational levels of the neutral and ion electronic states. From the spectrum, the upper limit of the ionization energy of the dimer is determined to be 43996 cm$^{-1}$, and the vibrational frequencies are measured to be 121 cm$^{-1}$ in the neutral state and 90 cm$^{-1}$ in the ion state. By combining with ab initio calculations at CASPT2 level, the ground state of Lu$_2$ is identified as $^3\Sigma_g^-$. The $^3\Sigma_g^-$ state has an electron configuration of 6s$\sigma_g^2$5d$\pi_u^1$5d$\pi_u^1$6s$\sigma_u^2$, which is formed by the interactions of two Lu atoms in the $^2$D(5d6s$^2$) ground state. Ionization of the neutral state removes a 5d$\pi$$_u$ bonding electron and yields a ion state with a considerably longer bond distance. Lu$_2$ has a very different bonding feature from La$_2$, for which a $^1\Sigma_g^+$ ground state was previously identified with an electron configuration of 5d$\pi_u^4$6s$\sigma_g^2$ formed by the interactions of two La atoms in the $^4$F(5d$^2$6s) excited state. \textbf{135}, 034309 (2011).}
UBIQUITOUS INTERSTELLAR MOLECULES WITH RADICALLY DIFFERENT CATION STRUCTURES: INFRARED SPECTROSCOPY OF FORMALDEHYDE AND METHANOL CATIONS
(Ohio State University, 2013) Mosley, Jonathan D.; Duncan, Michael A.
Formaldehyde and methanol are detected in interstellar and circumstellar sources by rotational transitions resulting from their well-known structures. For the radical cations with nominal formulas $[C,H_2,O]^+$ and $[C,H_4,O]^+$, no such measurements have been made in interstellar sources or in the laboratory to our knowledge. We measured the infrared spectrum of both radical cations in the gas phase using infrared photodissociation spectroscopy and found structures that differ drastically from the neutral closed shell species. For the case of $[C,H_2,O]^+$, formaldehyde cation $CH_2O^+$ and hydroxymethylene cation $CHOH^+$ are predicted to be minima with only ~5 kcal/mol difference in stability. We see evidence for two isomers in the infrared spectrum and investigate the effects of the argon tag on these small (four atoms) radical cations. For the mass 32 cation $[C,H_4,O]^+$, theory predicts the methyleneoxonium cation $CH_2OH_2^+$ to be about 15 kcal/mol more stable than the methanol cation $CH_3OH^+$. We present definitive assignments of vibrational features to these two isomers of the mass 32 cation. We discuss the kinetic trapping occurring in the ion source that produce the thermodynamically unfavorable $CH_3OH^+$ simultaneously with the lowest energy structure, $CH_2OH_2^+$. The application of our findings to astrochemistry is discussed.
THE CORONENE VIBRONIC STATES ABOVE THE FIRST IONIZATION POTENTIAL INVESTIGATED THROUGH TPEPICO EXPERIMENTS
(Ohio State University, 2013) Brechignac, Ph.; Falvo, C.; Parneix, P.; Pino, T.; Pirali, O.; Garcia, G.; Nahon, L.; Joblin, C.; Kokkin, D.; Bonammy, A.; Mulas, G.
Threshold Photoelectron spectra (TPES), as well as Total Ion Yeld (TIY) spectra of jet-cooled Coronene ($C_{12}H_{24}$) have been obtained using the electron/ion coincidence imaging spectrometer DELICIOUS II available at the DESIRS beamline of the French Synchrotron facility SOLEIL. The obtained data can be interpreted in the light of new theoretical DFT and TDDFT based calculations. They will be discussed in comparison to available photoelectron (PES) and optical absorption data. New autoionizing neutral states have also been observed and their relaxation to final cationic states characterized.
INFRARED SPECTROSCOPY OF THE MASS 43 CATION: ACETYL CATION AND PROTONATED KETENE
(Ohio State University, 2013) Mosley, Jonathan D.; Duncan, Michael A.
The mass 43 cation $[C_2,H_3,O]^+$ is prominent in mass spectra of organic molecules. Theory predicts no less than nine structural isomers, and the acetyl cation $CH_3CO^+$ is the global minimum. The infrared spectrum of the mass 43 cation from methyl acetate shows vibrations only from the acetyl cation. The effects of the methyl free internal rotor are discussed. The mass 43 cation from acetone shows evidence for both the acetyl cation and the less thermodynamically stable (~50 kcal/mol) protonated ketene isomer $CH_2COH^+$. The effects of varying the kinetic trapping conditions in our ion source on isomeric ratios of the mass 43 cation are discussed.
HIGH PRECISION SPECTROSCOPY OF CH$_5^+$ USING NICE-OHVMS
(Ohio State University, 2013) Hodges, James N.; Perry, Adam J.; McCall, Benjamin J.
The elusive methonium ion, CH$_5^+$, is of great interest due to its highly fluxional nature. The only published high-resolution infrared spectrum remains completely unassigned to this date. (1999) \textbf{284}, 135--137. } The primary challenge in understanding the CH$_5^+$ spectrum is that traditional spectroscopic approaches rely on a molecule having only small (or even large) amplitude motions about a well-defined reference geometry, and this is not the case with CH$_5^+$. \vspace{1em} We are in the process of re-scanning Oka's spectrum, in the original Black Widow discharge cell, using the new technique of Noise Immune Cavity Enhanced Optical Heterodyne Velocity Modulation Spectroscopy (NICE-OHVMS). \emph{Opt. Express} (2011), \textbf{19}, 24822--24827.} \emph{Chem. Phys. Lett.} (2012), \textbf{551}, 1--6.} The high precision afforded by optical saturation in conjunction with a frequency comb allows transition line centers to be determined with sub-MHz accuracy and precision -- a substantial improvement over the 90 MHz precision of Oka's work. \vspace{1em} With a high-precision linelist in hand, we plan to search for four line combination differences to directly determine the spacings between rotational energy levels. Such a search is currently infeasible due to the large number of false positives resulting from the relatively low precision and high spectral density of Oka's spectrum. The resulting combination differences, in conjunction with state-of-the-art theoretical calculations from Tucker Carrington,, (2008), \textbf{129}, 234102.} may provide the first insight into the rotational structure of this unique molecular system.
SUB-DOPPLER SPECTROSCOPY OF H$_3^+$
(Ohio State University, 2013) Hodges, James N.; Perry, Adam J.; Siller, Brian M.; McCall, Benjamin J.
Spectroscopy of H$_3^+$ is of fundamental interest for advancing \textit{ab initio} efforts to calculate spectra with high precision and accuracy. H$_3^+$ is the simplest polyatomic ion, which is why it is an excellent benchmark for theory. In order to perform calculations with spectroscopic accuracy, relativistic and non-adiabatic corrections to the Born-Oppenhiemer approximation must be included; calculations with these considerations agree to within hundredths of a wavenumber. (1999), \textbf{110}, 5056--5064.} Increasing the precision of the calculations further will require a treatment of quantum electrodynamic effects, as has already been implemented for the diatomic case, \emph{J. Chem. Theor. Comp.} (2011), \textbf{7}, 3105--3115.} and testing these calculations will require higher-precision experimental data to guide \textit{ab initio} calculations. \vspace{1em} Noise Immune Cavity Enhanced Optical Heterodyne Velocity Modulation Spectroscopy, or NICE-OHVMS \emph{Opt. Express} (2011), \textbf{19}, 24822--7.} \emph{Chem. Phys. Lett.} (2012), \textbf{551}, 1--6.}, is a highly sensitive, highly precise technique that we have employed to observe transitions in the $\nu_2$ fundamental band of H$_3^+$. It combines the advantages of cavity enhancement and heterodyne detection with the ion-neutral discrimination afforded by velocity modulation. Combining a cavity with a high power mid-infrared light source, we can saturate rovibrational transitions. The resulting Lamb dips may be fit in order to determine line centers to a much higher precision than is possible for ordinary Doppler broadened profiles. Additionally, a frequency comb is used to surpass the limited accuracy and precision of a wavemeter. Here we present the results from comb calibrated H$_3^+$ transitions observed via NICE-OHVMS. Precision and accuracy of $\sim$ 1 MHz were achieved representing the most accurate and precise H$_3^+$ line list that has been obtained to date.
PRECISION LASER SPECTROSCOPY OF H$_3^+$
(Ohio State University, 2013) Chen, Hsuan-Chen; Peng, Jin-Long; Amano, T.; Shy, Jow-Tsong
The high-resolution sub-Doppler Lamb dips of the $\nu_2$ fundamental band transitions of H$_3^+$ have been observed using an extended negative glow discharge tube as an ion source and a periodically poled lithium niobate optical parametric oscillator as a radiation source.,{~\bf 109},~263002~(2012)} The absolute frequencies of five transitions were measured to an accuracy of 250 kHz using a fiber optical frequency comb. In addition, we measured the homogeneous linewidths of these lines. Physical significance of these results will be discussed in terms of collisional processes.
INFRARED SPECTROSCOPY OF JET COOLED ND$_2$H$_2^{+}$ MOLECULAR IONS: THE SYMMETRIC AND ANTISYMMETRIC NH STRETCH MODES
(Ohio State University, 2013) Chang, Chih-Hsuan; Nesbitt, David J.
Rovibrational progressions in the symmetric ($v$$_6$) and antisymmetric ($v$$_1$) NH stretching modes of the ND$_2$H$_2^{+}$ molecular ion are observed for the first time, exploiting the i) high ion density and ii) high resolution capabilities of our slit jet discharge infrared spectrometer. These isotopomeric ions are generated by striking a modulated (50 KHz) electrical discharge in a mixture of ND$_3$/H$_2$O/H$_2$ gases, achieving a modulated ion density suitable for time-gated, lock-in detection in the throat of a long path slit-jet expansion. Assignment of both $b$-type and $c$-type bands enables high accuracy determination of the rotational constants ($A$$^{\prime\prime}$=4.85598(19), $B$$^{\prime\prime}$=3.96811(11), and $C$$^{\prime\prime}$=3.44661(40) cm$^{-1}$), with band origins for $v$$_1$ and $v$$_6$ modes determined to be 3297.54367(34) and 3337.90456(33) cm$^{-1}$, respectively. The results prove to be in good agreement with anharmonically corrected predictions from ${ab}$ initio quartic force fields of Martin and Lee.
SUB-DOPPLER SPECTROSCOPY OF ND$_3$H$^{+}$ ION IN THE NH STRETCHING MODE
(Ohio State University, 2013) Chang, Chih-Hsuan; Buckingham, Grant T.; Nesbitt, David J.
Despite early successes with velocity modulation spectroscopy$^{,}$of ammonium (NH$_4^{+}$ ) and perdeuteroammonium (ND$_4^{+}$) cation, corresponding studies of any of the mixed H/D isotopomers (NH$_m$D$_{4-m}^{+}$) have proven elusive. In this talk, we present first high resolution results on the lone NH stretch fundamental mode for the jet cooled ND$_3$H$^{+}$ ion, based on tunable IR difference frequency absorption spectroscopy in a slit jet, sub-Doppler resolution infrared spectrometer. Supersonically cooled ND$_3$H$^{+}$ ions are generated by modulated (50 KHz) discharges (650V, 500 mA) in ND$_3$ doped H$_2$/Ne slit jet expansions, monitored by time-gated, lock-in detection methods and with absorption sensitivities near the quantum shot noise limit. Jet cooled (30 K) $P$, $Q$, and $R$ branch rovibrational progressions in the $a$-type NH stretch band are observed and unambiguously assigned by four line ground state combination differences, with additional confirmation by nuclear spin statistical weights for the 3 identical D atoms (I = 1). Least squares fits to this parallel band yield precision rotational constants and an NH stretch vibrational band origin at 3316.8347(19) cm$^{-1}$. These high resolution spectroscopic results prove to be in generally excellent agreement with high level ${ab}$ initio theoretical predictions by Martin and Lee.

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