In the last symposium and a recent paperW. Chen, K. Kawaguchi, P. F. Bernath, and J. Tang, J. Chem. Phys. 142, 064317 (2015). we reported a simultaneous analysis for the Phillips and Ballik-Ramsay band systems with a deperturbation treatment for the X¹Σ⁺ and b³Σ⁻ states of C₂ and also, for the first time, the observation of the forbidden transitions between the singlet and triplet states of C₂. In the present study, we consider the interaction between the a³Π and c³Σ⁻ states to remove some anomalies in the higher order constants of the a³Π state presented in the previous work. The local interaction between the a³Π v=7 and c³Σ⁻ v=1 states was considered in a recent analysisM. Nakajima and Y. Endo, J. Mol. Spectrosc. 302, 9 (2014).or the perturbation of the spectrum. We consider the interaction between all the vibrational levels of the two electronic states with a set of Dunham-like constants. The progress and results will be presented. W. Chen, K. Kawaguchi, P. F. Bernath, and J. Tang, J. Chem. Phys. 142, 064317 (2015)., M. Nakajima and Y. Endo, J. Mol. Spectrosc. 302, 9 (2014).f

Spectroscopic data for the A ³Π₁ and X ¹Σ⁺ states of I^35/37Cl have been obtained by many researchers using grating spectrometers and Fourier-transform infrared spectrometers. J.A.\ Coxon, R.M. Gordon and M.A. Wickramaaratchi, J. Mol. Spectr.  79 (1983) 363, 380.^, H. Hedderich P.F. Bernath andG.A. McRae J. Mol. Spectr. 155 (1992) 384.In a previouspaper T.Yukiya, N. Nishimiya and M. Suzuki, J. Mol. Spectr.\269 (2011) 193.e reported the measurement of doppler limitedelectronic vib−rotational absorption lines of the A ^3_1 X ^1^+ system of I^35/37Cl using a sourcemodulation method, and new Mass−reduced Dunham coefficients were reportedfor the X−state. However, it is becoming increasingly common to analysediatomic molecule spectroscopic data using the "direct−potential−fit"(DPF) method in which observed transition energies are fitted to simulatedspectra generated from analyic models for the potential energy function(s).This method tends to require fewer fitting parameters than traditionalDunham analyses, as well as having more robust extrapolation propertiesin both the v and J domains. The present work combines all availablepreviously reported data for the A ^3_1 and X ^1^+states with new measurements up to v'=10 in the 0.7m region obtained with atone burst method using a Ti:Sapphire Ring Laser (M Squared Ltd SolsTis CWwith Tera scan) in the the first DPF analysis reported for this system.The results of this study and our new fully analytic potential energyfunctions for the A ^3_1 and X ^1^+ H.Hedderich P.F. Bernath andG.A. McRae J.Mol.Spectr.155 (1992) 384.T.Yukiya, N. Nishimiya and M. Suzuki, J.Mol.Spectr.\269 (2011) 193.w

Spectroscopic data involving levels lying near the dissociation limit are very important for determining accurate molecular well depths and full potential energy curves. In previous work, we have reported the potential functions and values of parameters D_e and r_e for the A ³Π₁ and X ¹Σ⁺ states of IBr.T.Yukiya, N. Nishimiya, M. Suzuki and R.J. Le Roy, paper MG03 at the 69^th International Symposium on Molecular Spectroscopy, University of Illinois (2014)hat study used data extending to v′(A)=29 and determined anomalous fluctuations in the v-dependence of the first differences of ∆B_v=B_v+1−B_v for levels v′=27−29 of the A ³Π₁ state which, surprisingly, seems to have been smoothly accounted by a fitted potential energy function that shows no visually perceptible irregularities. In the present work, a Ti:Sapphire ring laser(M SQUARED LASERS Ltd. SolsTiS CW with Tera-scan) has been introduced to probe the 0.7μm region closer to the dissociation limit and examine whether the anomalous ∆B_v behaviour expends further up the well. The results of this study will be presented.

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T.Yukiya, N. Nishimiya, M. Suzuki and R.J. Le Roy, paper MG03 at the 69^th International Symposium on Molecular Spectroscopy, University of Illinois (2014)T

The near-infrared spectrum of nickel chloride, NiCl, has been recorded at high resolution using intracavity laser absorption spectroscopy. The NiCl molecules were produced in a plasma discharge of a nickel hollow cathode from a trace amount of CCl₄ using Ar as the sputter gas. Spectra were collected from 12,490-12,660 cm⁻¹and 13,200-13,350 cm⁻¹as a series of overlapping  5 cm⁻¹scans. The (0,1), (1,0), and (2,1) bands of the [13.0] ²Π_3/2-X ²Π_3/2 transition, System G, were observed at 12,537 cm⁻¹, 13,352 cm⁻¹, and 13,318 cm⁻¹, respectively. The (1,0) band of the [12.3] ²Σ⁻-X ²Π_3/2 transition, System H, was observed at 12,645 cm⁻¹. Analyses of these bands will be presented.

Emission spectra of yttrium monoiodide (YI) spanning the 250 - 940 nm spectral region were generated by the photodissociation of yttrium tri-iodide under photoexcitation at 248 nm (KrF laser). Fluorescent spectra in the13,000 - 19,000 cm⁻¹ and 24,000 - 40,000 cm⁻¹ regions will be first reported. New vibrational transitions of YI in the 20,000 - 25,000 cm⁻¹ interval will be presented as well.

HCP belongs to a class of reactive small molecules with much interest to spectroscopists. It bears certain similarities to HCN, including a strong Ã(bent) - ~X(linear) ultraviolet transition, associated with the HCP-HPC isomerization pathway. HCP has traditionally been generated by the in situ reaction of PH₃ and acetylene. In this talk, we will discuss a recently developed synthetic precursor molecule, 1,1-((triphenylphosphoranylidene)methyl)-9,10-phosphanoanthracene. At temperatures above 200 degrees Celsius, this precursor is thought to release HCP in a vibrationally excited state. We will present preliminary spectra on this system obtained by LIF and chirped pulse millimeter wave spectroscopy.

Determining full model potential energy functions for molecular states that have a `natural' rotationless barrier which protrudes above the potential asymptote, such as the B <sup>1</sup>Π<sub>u</sub> states of alkali dimers, is a challenging problem. The present work extends our previous Direct-Potential-Fit (DPF) analysis of data for the B <sup>1</sup>Π<sub>u</sub> state of Li<sub>2</sub> Y. Huang and R.J. Le Roy, J. Chem. Phys., 119, 7398 (2003)y introducing a more sophisticated model for the long-range tail of the fully analytic `Double Exponential Long-Range' (DELR) potential function form^a that takes account of the interstate coupling that occurs near the asymptotes of nS+nP alkali dimers. M. Aubert-Frécon and G. Hadinger and S. Magnier and S. Rousseau, J. Mol. Spectosc., 288, 182 (1998).his type of analysis is then applied to data for the B ¹Π_u state of Rb₂, and a concurrent extension of the DPF analysis of Seto and Le RoyJ.Y. Seto and R.J. Le Roy, J. Chem. Phys., 113, 3067 (2000).ields an improved fully analytic potential energy function for its ground X ¹Σ_g⁺ state. The effect of taking account of the long-range inter-state coupling on the shapes of the outer walls of the B ¹Π_u state potential functions for these two species will also be examined.

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 Y. Huang and R.J. Le Roy, J. Chem. Phys., 119, 7398 (2003)b  M. Aubert-Frécon and G. Hadinger and S. Magnier and S. Rousseau, J. Mol. Spectosc., 288, 182 (1998).T J.Y. Seto and R.J. Le Roy, J. Chem. Phys., 113, 3067 (2000).y

A new laser spectroscopic technique has been demonstrated for examining the structure of alkali-rare gas diatomic electronic states near the classical limit. In two-color experiments, Rb-Ar or Rb-Kr thermal pairs are excited by free←free or bound←free transitions while monitoring the amplified spontaneous emission produced on the Rb D₁ or D₂ lines. Spectra observed lying within 10 cm⁻¹ of the separated atom limit for the A²Π_1/2 states of Rb-Ar and Rb-Kr will be presented and discussed.

Collision-induced absorption spectra can be calculated quantum mechanically and from first principles. However, such calculations are usually performed in the approximation of an isotropic interaction potential and neglecting exchange effects. We present theory for including exchange and anisotropic interactions in the calculation of collision-induced absorption spectra, and apply this method to the H₂−H₂ and N₂−N₂ systems. For H₂−H₂, the isotropic interaction approximation is generally accurate, although significant effects of anisotropic interactions are observed in the far wing of the spectrum. For N₂−N₂, anisotropic interactions increase the line strength at low energy by two orders of magnitude. The agreement with experimental data is reasonable in the isotropic interaction approximation, and improves when the full anisotropic potential is considered. The effect of the interaction anisotropy decreases at higher energy, which validates the usual isotropic interaction approximation as a high-temperature approximation for the calculation of collision-induced absorption spectra.

Around 398 nm, the jet-cooled NO₂ spectrum exhibits a well identified dissociation threshold (D₀). Combining LIF detection and continuous-wave absorption-based CRDS technique a frequency range of  ∼ 25 cm⁻¹ is analyzed at high resolution around D₀. In addition to the usual rovibronic transitions towards long-lived energy levels,  ∼ 115 wider resonances are observed. Over this energy range, the resonance widths spread from  ∼ 0.006 cm⁻¹ ( ∼ 450 ps) to  ∼ 0.7 cm⁻¹ ( ∼ 4 ps) with large fluctuations. At least two ranges of resonance width can be identified when increasing the excess energy. They are associated with the opening of the dissociation channels NO₂→NO(X ²Π_1/2, v=0, J=1/2)+O(³P₂) and NO₂→NO(X ²Π_1/2, v=0, J=3/2)+O(³P₂). Weighted mean unimolecular dissociation rate coefficients k_uni are calculated. The density of reactants (following the RRKM predictions) is deduced, and it will be discussed versus the density of transitions, the density of resonances and the density of vibronic levels. The data are analyzed in the light of time-resolved data previously reported. This analysis corroborates the existence of loose transition states along the reaction path close to the dissociation energy in agreement with the phase space theory predictions[Accpeted in J. Chem. Phys.]

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[Accpeted in J. Chem. Phys.].

Knowledge of CO₂-broadened HDO widths and their temperature dependence exponents are required to interpret atmospheric spectra of Mars and Venus. We therefore used nine high-resolution, high signal-to-noise spectra of HDO and HDO+CO₂ mixtures to obtain broadening coefficients for selected transitions of the ν₂ and ν₃ vibrational bands located at 7.13 and 2.70 μm, respectively. The gas samples were prepared by mixing equal amounts of high-purity distilled H₂O and a 99% enriched D₂O sample. Spectra at different temperatures (255-296 K) were obtained using a 20.38 cm long coolable cellK. Sung, A.W. Mantz, M.A.H. Smith, L.R. Brown, T.J. Crawford, V.M. Devi, D.C. Benner. J. Mol. Spectrosc. 162 (2010) 124-134.nstalled in the sample compartment of the Bruker 125HR Fourier transform spectrometer at the Jet Propulsion Laboratory, in Pasadena, CA. The retrieved parameters included accurate line positions, intensities, self- and CO₂-broadened half-width and pressure-shift coefficients and the temperature dependences of CO₂ broadened HDO. The spectroscopic parameters for many transitions were obtained simultaneously by multispectrum fittingD.C. Benner, C.P. Rinsland, V. Malathy Devi, M.A.H. Smith, and D. Atkins. JQSRT 53 (1995) 705-721.f all nine spectra in each band. A non-Voigt line shape with speed dependence was applied. Line mixing was also observed for several transition pairs. Preliminary results will be compared to other recent measurements reported in the literature.Research described in this paper are performed at the College of William and Mary, Jet Propulsion Laboratory, California Institute of Technology, Connecticut College and NASA Langley Research Center under contracts and cooperative agreements with the National Aeronautics and Space Administration.html:<hr /><h3>Footnotes: K. Sung, A.W. Mantz, M.A.H. Smith, L.R. Brown, T.J. Crawford, V.M. Devi, D.C. Benner. J. Mol. Spectrosc. 162 (2010) 124-134.i D.C. Benner, C.P. Rinsland, V. Malathy Devi, M.A.H. Smith, and D. Atkins. JQSRT 53 (1995) 705-721.o Research described in this paper are performed at the College of William and Mary, Jet Propulsion Laboratory, California Institute of Technology, Connecticut College and NASA Langley Research Center under contracts and cooperative agreements with the National Aeronautics and Space Administration.

The laser induced fluorescence ( LIF ) spectrum of à ²∆ - X̃ ²Π transition was obtained for SiCN generated by laser ablation under supersonic free jet expansion. The vibrational structure of the dispersed fluorescence ( DF ) spectra from single vibronic levels ( SVL's ) was analyzed with consideration of Renner-Teller ( RT ) interaction. The usual analysis based on the perturbation approachJ. M. Brown and F. Jørgensen, Advances in Chemical Physics 52, 117 (1983). indicated considerably different spin splitting for the μ and κ levels of the X̃ ²Π state of SiCN, in contrast to identical spin splitting for general species based on the usual RT analysis. Further analysis of the vibrational structure is being carried out via direct RT diagonalization.

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J. M. Brown and F. Jørgensen, Advances in Chemical Physics 52, 117 (1983).,

The internal force field of ~C¹B₂ state of SO₂ is determined up to quartic terms. The fit incorporates observed vibrational energy levels of both S¹⁶O₂ and S¹⁸O₂ below 3000 cm⁻¹, as well as rotational information of both isotopologues. With inclusion of nine recently observed B₂ symmetry levels of S¹⁶O₂ in the fit, the double-well potential in asymmetric stretching coordinate can be better characterized. By inspecting the wavefunctions, as well as the basis state distribution of the eigenvectors, we are able to give vibrational assignments to majority of states in this energy region, based on Kellman's semiclassical study on fermi-resonant systems. Our analysis calls into question the validity of previous assignments of several vibrational levels. In addition, the force field allows us to calculate Coriolis matrix elements between vibrational bands, and the calculated values agree well with experimentally derived values. In particular, it predicts and explains why the experimental values are always much smaller than numbers predicted based on a naive harmonic picture. Our work is a first step towards a more complete understanding of the ~C state potential energy surface near the equilibrium geometry and it is relevant to the question of how vibronic coupling between ~C¹B₂ state and higher lying A₁ state(s) gives rise to unequal S-O bond length.

A new study of ¹³CH₄line positions and intensities in the Octad region between 3600 and 4800 cm⁻¹will be reported. Nine spectra were recorded with two Fourier transform spectrometers (the McMath-Pierce FTS at Kitt Peak Observatory and the Bruker 125 HR FTS at the Jet Propulsion Laboratory) using ¹³C-enriched samples at temperatures from 299 K to 80 K. Line positions and intensities were retrieved by non-linear least squares curve-fitting procedures and analyzed using the effective Hamiltonian and the effective Dipole moment expressed in terms of irreducible tensor operators adapted to spherical top molecules. Quantum assignments were found for all the 24 sub-vibrational states of the Octad (some as high as J=10). Over 4750 experimental line positions and 3300 line intensities were fitted with RMS standard deviations of 0.004 cm⁻¹and 6.9%, respectively. A new linelist of over 9600 measured positions and intensities from 3607 to 4735 cm⁻¹was produced, with known quantum assignments given for 45% of the features.^{a a} Part of the research described in this paper was performed at the Jet Propulsion Laboratory, California Institute of Technology, NASA Langley Research Center, and Connecticut College, under contracts and cooperative agreements with the National Aeronautics and Space Administration. The support of the Groupement de Recherche International SAMIA between CNRS (France) and RFBR (Russia) is acknowledged.

Modern techniques of quantum chemistry allow the prediction of molecular properties to good accuracy, provided the systems are small and their electronic structure is not too complex. For most users of common program packages, `chemical' accuracy in the order of a few kJ/mol for relative energies between different geometries is sufficient. The demands of molecular spectroscopists are typically much more stringent, and often include a detailed topographical survey of multi-dimensional potential energy surfaces with an accuracy in the range of wavenumbers. In a benchmark study of current predictive capabilities we pick the slightly sophisticated, but conceptually simple and well studied case of the Na₃ ground state, and present a thorough investigation of the interplay between Jahn-Teller-, spin-orbit-, rovibrational- and hyperfine-interactions based only on ab initio calculations. The necessary parameters for the effective Hamiltonian are derived from the potential energy surface of the 1²E^′ ground state and from spin density evaluations at selected geometries, without any fitting adjustments to experimental data. We compare our results to highly resolved microwave spectra.L. H. Coudert, W. E. Ernst and O. Golonzka, J. Chem. Phys. 117, 7102–7116 (2002)html:<hr /><h3>Footnotes: L. H. Coudert, W. E. Ernst and O. Golonzka, J. Chem. Phys. 117, 7102–7116 (2002)