r0pt Figure At first glance dicarbon, C₂, would appear to be a very simple homonuclear diatomic molecule. However the bonding structure of C₂ has long been a topic of debate, with different qualitative theories predicting a C−C bond order of 2, 3, or even 4R. M. Macrae, Sci. Prog. 99, 1 (2016) Recent evidence for a quadruply bonded dicarbon has been provided by multiconfigurational ab-initio calculationsS. Shaik, D. Danovich, W. Wu, P. Su, H. Rzepa, P. Hiberty, Nat. Chem. 4, 195 (2012) However, the interpretation of these calculations has caused debate, with some research preferring the notion of a double, triple, or quasi double-triple bond, while other studies note that there is not enough evidence to clearly define the bonding nature of C₂R. Zhong, M.Zhang, H. Xu, Z. Su, Chem. Sci. 7, 1028 (2016) In this work, photoelectron spectra of the C₂⁻ anion are measured using a high resolution photoelectron imaging (HR-PEI) spectrometer. The electron anisotropy of the detachment reveals the character of the parent anion orbital. Detachment to both the ground X̃ ¹Σ_g⁺ and first excited ã ³Π_u electronic states is observed, identifying the character of two orbitals: the diffuse detachment orbital of the anion, and the HOMO of the neutral. The measurements show that electron detachment occurs from a pure s-like orbital (3σ_g) and a dominant p-like orbital (1π_u), that is inconsistent with the predictions of strongly mixed (50:50) sp orbitals required for the high bond order models, a result compatible only with the predictions of a C=C double bonding scheme. R. M. Macrae, Sci. Prog. 99, 1 (2016). S. Shaik, D. Danovich, W. Wu, P. Su, H. Rzepa, P. Hiberty, Nat. Chem. 4, 195 (2012). R. Zhong, M.Zhang, H. Xu, Z. Su, Chem. Sci. 7, 1028 (2016).

Nascent CO (X ¹Σ⁺) photoproducts formed in the dissociation of OCS at 215 nm were probed using 2+1 resonance enhanced multiphoton ionization (REMPI) through the E ¹Π state. This photodissociation produces a highly rotationally excited CO distribution, with fragment rotational levels ranging from J=48 to J=77. The resulting REMPI spectrum contains a prominent Q branch, despite negligible line strength factors for high J, two-photon, Π-Σ, Q branch transitions. The presence of a Q branch in the spectrum is explained by intensity borrowing from the nearby C ¹Σ⁺ state, as coupling between the C and E states is well documented, and two photon, Σ-Σ, Q branch transitions are intense for high J states. The observed relative intensities of the Q and S branch lines are well described by extrapolation to high J of the J-dependent mixing of C and E states inferred from the E state lambda doublet splittings at lower J. Improved D_e and D_f constants have been derived through the incorporation of this high J data.

The electronic spectrum of CaH has been studied for over 90 years. The first laboratory spectroscopy of CaH was carried out in 1925 on C²Σ⁺ - X²Σ⁺ transitions in the near-UV regionR. S. Mulliken, Phys. Rev. 25, 509 (1925). Our primary interest is the B state and how it is affected by other nearby states. The B state has a double−minimum potential energy function. For this state we can identify three energy regimes. The lowest is the energy range between the minimum of the inner well and the minimum of the higher lying outer well. In this lowerenergy region the B−X and A−X spectra were recently investigated by Shayestech et al.A. Shayesteh, R.S. Ram, P.F. Bernath, J. Mol. Spectrosc. 288, 46 (2013). The high energy range is that lying above the potential energy barrier between the two wells. Our previous laser induced fluorescence report was on the vibrational states in this higher energy range.K. Watanabe, N. Yoneyama, K. Uchida, K. Kobayashi, F. Matsushima, Y. Moriwaki, S. C. Ross, Chem. Phys. Lett. 657, 1 (2016).In that previous report we were able to confirm a strong irregularity in the vibrational energyspacings that had been previously predicted by the ab initio study of Carlsund−Levin et al.. This irregularity isdue to interaction between the B and D states.C. Carlsund-Levin, N. Elander, A. Nunez, A. Scrinzi, Phys. Scripta 65, 306 (2002). In the current study we have investigated the intermediate energy regime. These are energies starting from somewhat below the minimum of the higher lying outer well and continuing up to somewhat above the potential energy barrier between the two wells. In this intermediate energy range we have identified the A-X(4,0) and B-X(3 or 5, 0) bands. We present evidence for possible interactions between these vibrational levels. We will report on the current status of our work as we continue our program of delineating the vibrational levels of the B state over a full energy range: starting at the energy of the minimum of the inner well, progressing through the energy of the minimum of the outer well, the energy of the barrier, and on towards the dissociation limit.

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R. S. Mulliken, Phys. Rev. 25, 509 (1925).\end A. Shayesteh, R.S. Ram, P.F. Bernath, J. Mol. Spectrosc. 288, 46 (2013). K. Watanabe, N. Yoneyama, K. Uchida, K. Kobayashi, F. Matsushima, Y. Moriwaki, S. C. Ross, Chem. Phys. Lett. 657, 1 (2016).\end C. Carlsund−Levin, N. Elander, A. Nunez, A. Scrinzi, Phys. Scripta 65, 306 (2002).

Detailed information on the absorption and emission spectra of satellite plume constituents is lacking. Fluorocarbons are used as a space vehicle propellant in cold gas and pulsed plasma thrusters. Consequently, these uses likely produce small fluorocarbon radicals through pyrolysis and solar driven photolysis. Specifically, it’s been shown that certain VUV wavelengths can produce electronically excited CF₃ radicals from parent fluorocarbons,Washida, N., Suto, M., Nagase, S., Nagashima, U., Morokuma, K., J. Chem Phys. 78, 1025, (1983).ut it has not been shown if ground state CF₃ radicals may be produced as well. Furthermore, the CF₃ radical’s laser induced fluorescence spectrum has never been reported. Here we investigate the photosynthesis of CF₃ radical from VUV excitation of fluorocarbons, the direct fluorescence from the CF₃ radical, and the radical’s relevance in the space environment.

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Footnotes:

Washida, N., Suto, M., Nagase, S., Nagashima, U., Morokuma, K., J. Chem Phys. 78, 1025, (1983).b

DUO is a program designed to solve a coupled Schrödinger equation for the motion of nuclei of a given diatomic molecule characterized by an arbitrary set of electronic states. S.N. Yurchenko, L. Lodi, J. Tennyson, and A.V. Stolyarov, Comput. Phys. Commun. 202, 262 (2016).Duo is capable of both refining potential energy curves (by fitting data to experimental energies or transition frequencies) and producing line lists. Our most recent results of applying DUO to produce hot line lists for open-shell diatomic molecules include NO,A. Wong, S. N. Yurchenko, P. Bernath, H. S. P. Mueller, S. McConkey, and J. Tennyson, Mon. Not. R. Astron. Soc. 470, 882 (2017).iH,S. N. Yurchenko, F. Sinden, L. Lodi, C. Hill, M. N. Gorman, and J. Tennyson, Mon. Not. R. Astron. Soc. 473, 5324 (2018)S and PO,L. Prajapat, P. Jagoda, L. Lodi, M. N. Gorman, S. N. Yurchenko, and J. Tennyson, Mon. Not. R. Astron. Soc. 472, 3648 (2017).₂,S. N. Yurchenko, J. Tennyson, and et al, Mon. Not. R. Astron. Soc. in preparation (2018).N and SH,S. N. Yurchenko, W. Bond, M. N. Gorman, L. Lodi, L. K. McKemmish, W. Nunn, R. Shah, and J. Tennyson, Mon. Not. R. Astron. Soc. submitted (2018)nd AlH.H. Williams, P. C. Leyland, L. Lodi, S. N. Yurchenko, and J. Tennyson, Mon. Not. R. Astron. Soc. in preparation (2018).he published version of DUO only considers truly bound states. We are now working on extending DUO to treat quasi-bound or resonance states, or indeed the continuum itself, using the stabilization method.A.U. Hazi, H.S. Taylor, Phys. Rev. A 1, 1109 (1970)s an illustration, we present simulations of spectra of the quasi-bound system A ¹Π - X ¹Σ⁺ of AlH and of the continuum system A ¹Π - X ¹Σ⁺ and B ¹Σ⁺ - X ¹Σ⁺ of NaCl.

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Footnotes:

S.N. Yurchenko, L. Lodi, J. Tennyson, and A.V. Stolyarov, Comput. Phys. Commun. 202, 262 (2016). A. Wong, S. N. Yurchenko, P. Bernath, H. S. P. Mueller, S. McConkey, and J. Tennyson, Mon. Not. R. Astron. Soc. 470, 882 (2017).S S. N. Yurchenko, F. Sinden, L. Lodi, C. Hill, M. N. Gorman, and J. Tennyson, Mon. Not. R. Astron. Soc. 473, 5324 (2018)P L. Prajapat, P. Jagoda, L. Lodi, M. N. Gorman, S. N. Yurchenko, and J. Tennyson, Mon. Not. R. Astron. Soc. 472, 3648 (2017).C S. N. Yurchenko, J. Tennyson, and et al, Mon. Not. R. Astron. Soc. in preparation (2018).S S. N. Yurchenko, W. Bond, M. N. Gorman, L. Lodi, L. K. McKemmish, W. Nunn, R. Shah, and J. Tennyson, Mon. Not. R. Astron. Soc. submitted (2018)a H. Williams, P. C. Leyland, L. Lodi, S. N. Yurchenko, and J. Tennyson, Mon. Not. R. Astron. Soc. in preparation (2018).T A.U. Hazi, H.S. Taylor, Phys. Rev. A 1, 1109 (1970)A

Trifluoroacetic sulfuric anhydride, CF₃COOSO₂OH, has been produced under supersonic jet conditions from the reaction of sulfur trioxide and trifluoroacetic acid. The rotational spectra for both the parent and deuterated isotopologues have been recorded, but were notably weaker than similar spectra obtained for other carboxylic sulfuric anhydrides. The spectra were readily fit to a Watson A-reduced Hamiltonian with no evidence of internal rotation. M06-2X/6-311++G(3df,3pd) calculations indicate that the formation of CF₃COOSO₂OH proceeds through a π₂ + π₂ + σ₂ cycloaddition mechanism analogous to that previously established for other carboxylic sulfuric anhydrides. The barrier to formation for CF₃COOSO₂OH calculated at the CCSD(T)/CBS(D-T) level is slightly positive ( 0.7 kcal/mol), in contrast to the slightly negative value obtained for the formation of its acetic acid analog (acetic sulfuric anhydride). The possible role of internal rotation in the formation of both systems will be discussed.

Rotational spectra of two conformers of thioacetic acid (CH₃COSH) have been observed by pulsed-nozzle Fourier transform microwave spectroscopy. Spectroscopic constants are reported for both the syn- and anti- forms of the parent species, as well as for five isotopologues which include ³⁴S and ¹³C substitution on the methyl and carboxyl atoms. Spectra were fit using two different internal rotation fitting programs, XIAM and BELGI-Cs, and comparisons between their performances will be discussed. The experimental internal rotation barriers for the parent syn- and anti-thioacetic acid obtained from BELGI-Cs are 69.3(10) and 435.2(22) cm⁻¹, respectively, and compare favorably with the computed values of 83 and 344 cm⁻¹at the M06-2X/6-311+G(d,p) level of theory. An energy decomposition analysis using the block localized wavefunction method indicates that the steric (including both Pauli and electrostatic) repulsion between the -SH and CH₃ groups, which is further enhanced by the pi-conjugation from the -SH to the carbonyl group, is largely responsible for the large difference in the internal rotation barrier between the syn- and anti- forms.

Ruthenium tetroxide (RuO₄) is a heavy tetrahedral molecule characterized by an unusual volatility near ambient temperature. Because of its chemical toxicity and the radiological impact of its ¹⁰³Ru and ¹⁰⁶Ru isotopologues, the possible remote sensing of this compound in the atmosphere has renewed interest in its spectroscopic properties. In a recent study, the strong fundamental band associated with the excitation of the infrared active stretching mode ν₃ of ¹⁰²Ru¹⁶O₄, observed near 10 μm, was re-investigated at high-resolution (0.001 cm⁻¹) with the help of a ¹⁰²Ru isotopically pure sample.S. Reymond-Laruinaz, V. Boudon, L. Manceron, L. Lago, D. Doizi, J Mol Spectrosc 315 (2015) 46-54.uilding upon that work, the present contribution is the first investigation dealing with high-resolution line-by-line intensity measurements for the ν₃ fundamental band of ¹⁰²Ru¹⁶O₄. It relies on high resolution Fourier transform infrared spectra specifically recorded at room temperature at the AILES beam line of SOLEIL using synchrotron radiation, a specially constructed cell and an isotopically pure sample of ¹⁰²Ru¹⁶O₄. Relying on an effective Hamiltonian and associated effective dipole moment,^a the measured line intensities were assigned and dipole moment parameters determined. A HITRAN-formatted frequency and intensity line list was generated.

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Footnotes:

S. Reymond-Laruinaz, V. Boudon, L. Manceron, L. Lago, D. Doizi, J Mol Spectrosc 315 (2015) 46-54.B

Here we present some recent advances in frequency stabilized cavity ring-down spectroscopy (FS-CRDS) measurements of molecular line intensities of carbon dioxide in the (30012)← (00001), the (30013)←(00001), and the (30014)←(00001) bands near 1.6 μm. These measurements were performed near 296K using a frequency stabilized cavity ringdown spectrometer [1]. Additional independent measurements were performed on a frequency agile rapid scanning (FARS) CRDS [2]. We have compared the line intensities obtained from Hartmann Tran Profile (HTP) fits of the measured spectra to several spectroscopic databases, including UCL (ie, HITRAN2016) [3]. The overall agreement between these results and the ab initio calculations of Zak et al is excellent [3], although some individual transitions show deviations of up to 1%. The intensities for the (30012)←(00001) show average agreement at the 0.1% level. Preliminary measurements on the (30013)←(00001), and the (30014)←(00001) bands in this region also show good agreement with the ab initio of Zak et al for the (30013)←(00001), but considerably poorer agreement for the (30014)←(00001) band. No significant J-dependence is observed for any of the three bands. This work demonstrates significant improvement in experimental determination of important CO₂ line intensities in the 1.6 μm region. It also demonstrates that it may be feasible for ab initio theory to provide sufficiently accurate results for global determinations of line intensities in the near future. [1] H. Lin, Z. D. Reed, V. T. Sironneau, and J. T. Hodges, J. Quant. Spectrosc. Radiat. Transfer 161, 11-20 (2015). [2] G. W. Truong, K. O. Douglass, S. E. Maxwell, R. D. van Zee, D. F. Plusquellic, J. T. Hodges, and D. A. Long, Nat. Photonics 7, 532-534 (2013). [3] E. J. Zak, J. Tennyson, O. L. Polyansky, L. Lodi, N. F. Zobov, S. A. Tashkun, and V. I. Perevalov, J. Quant. Spectrosc. Radiat. Transfer 189, 267-280 (2017).

This is a further report in a project to record high resolution IR data of the ¹³C and D substituted isotopologues of propane (see talks FA04, FA05 and TK08 at 2017 ISMS). Initially in CLS Cycle 23 (Jan-Jun, 2015) we recorded spectra of the ν₂₆ (B₂) C-Type band whose corresponding band in C₃H₈ is observed in Titan's Atmosphere.That band and others seen in the 550-950 cm⁻¹region were too perturbed by complex torsional splittings for analysis at this time. In this talk will give details on the first high resolution (∆ν = 0.00096 cm⁻¹) IR investigation of the spectrum in the Far-IR region. We recorded spectra during Cycle 25 (Jan-Jun, 2017) of the ν₉ (A₁) CCC skeletal bending mode near 367.2389 cm⁻¹. This has a B-type band structure and appears unperturbed. Spectra were recorded at pressures of 0.014, 0.056, 3.995 & 8.087 Torr in a 72m optical path at room temperature. We used the Bruker IFS-125HR on the Far-IR beamline of the CLS. The spectra were assigned both traditionally and with the aid of the PGOPHER program of Colin Western.C. Western, J. Quant. Spectrosc. & Rad. Transf. 186, 221 ff. (2017).e were able to assign over 8100 lines with up to K = 35 and J = 60 using both the 4 and 8 Torr data sets. The only available MW data on this molecule are the seven K = 0, J = 0-6 lines from Lide.Lide, J.Chem. Phys. 33, p.1514ff. (1960). We therefore had to use the present data to determine a new set of ground state constants that included centrifugal distortion terms for this molecule. We compare these experimentally determined values with both Lide's A, B, C values and the recent calculated ab initio values of Villa, Senent & Carvajal.Villa, Senent & Carvajal, PCCP 15, 10258 (2013).pper state constants have also been been derived that provide a good simulation of the observed spectra. The hope is that this data will be useful in identifying isotopic propane lines in Titan and other astrophysical objects.

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Footnotes:

C. Western, J. Quant. Spectrosc. & Rad. Transf. 186, 221 ff. (2017).W Lide, J.Chem. Phys. 33, p.1514ff. (1960).. Villa, Senent & Carvajal, PCCP 15, 10258 (2013).U

Only old IR and no MW data exist for this molecule.Friedman & Turkevich, J. Chem. Phys. 17, 1012 ff. (1949); McMurry, Thornton & Condon, J. Chem. Phys. 17, 918 ff. (1949); McMurry & Thornton, J. Chem. Phys. 19, 1014 ff. (1951).; Gayles & King, Spectrochim. Acta 21, 543 ff. (1965); Kondo & Saeki, Spectrochim. Acta 29A, 735 ff. (1973).ast year we reported (2017 ISMS, TK08) on the ν₂₀ (B₁) A-type band recorded in CLS Cycle 23 (Jan-May, 2016). This was the only band with easily assignable lines. Other bands were perturbed and not assignable at present. We assigned most of ν₂₀ and rotational constants were determined for this molecule. Our ν₂₀ data was limited in K and J values due to the pressure used and time limitations in that cycle. Also some small torsional perturbations may have affected the derived constants. From our recent studies ν₉ bands appear unperturbed for the other ¹³C and D isotopologues. Therefore we recorded that band for 2,2-D₂-Propane in the Far-IR at higher pressures in new experiments. The spectrum of the ν₉ (A₁) band (CCC bend) was recorded on the Far-IR beamline during CLS Cycle 27 (Jun-Dec, 2017). Spectra were recorded at 4.055 Torr (∆ν = 0.00096 cm-1) and 7.691 Torr (∆ν = 0.0020 cm-1) to see higher K and J transitions. An optical path of 72 m and a cell temperature of 265.75K were used. We assigned over 5900 lines with both traditional methods and the aid of the PGOPHER program of Colin Western.C. Western, JQSRT 186, 221 ff. (2017)ines up to K = 37 and J = 55 were assigned by using both pressure data sets. Improved rotational constants including the inertial and centrifugal distortional constants will be reported. This varied isotopic data should improve the r₀ structure.

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Friedman & Turkevich, J. Chem. Phys. 17, 1012 ff. (1949); McMurry, Thornton & Condon, J. Chem. Phys. 17, 918 ff. (1949); McMurry & Thornton, J. Chem. Phys. 19, 1014 ff. (1951).; Gayles & King, Spectrochim. Acta 21, 543 ff. (1965); Kondo & Saeki, Spectrochim. Acta 29A, 735 ff. (1973).L C. Western, JQSRT 186, 221 ff. (2017)L