Diffuse Interstellar Bands (DIBs) are absorption bands detected in diffuse clouds by optical observations. Although  ∼  600 DIBs have been found so far, only the five bands were assigned to the fullerene cation and the other bands are not identified yet. Recently, benzonitrile (C₆H₅CN) was detected in interstellar space by radio as the first aromatic compound [1]. Thus, thiophenoxy radical (C₆H₅S) is received much attentions as a candidate of DIBs, because sulfur is a dominant element of interstellar molecules. Fluorescence excitation spectra of the ²A₂-X ²B₁ electronic transition of C₆H₅S showed the origin band as the strongest peak [2]. However, in our previous work, absorption spectra of phenoxy radical (C₆H₅O) brought out the stronger vibronic bands than the origin band [3]. The fact suggests that intensities of higher vibronic bands of C₆H₅S are lost by radiationless transitions in the fluorescence excitation spectra. Thus, stronger vibronic bands of C₆H₅S are expected because of similarity of the two molecules. We investigated the vibronic bands in the 473-519 nm region by Cavity Ring Down spectroscopy and detected them. The strongest vibronic band at 4850 Å was assigned to the 6a₀² + 6b₀¹ transition. This band may appear as DIB if sufficient amount of this radical exists in interstellar medium. [1] McGuire et al., Science, 359, 202 (2018). [2] Shibuya et al., J. Chem. Phys. 121, 237 (1988). [3] Araki et al., Astronomical J. 150, 113 (2015).

Cosmic rays are mysterious particles mostly atomic nuclei with extremely high energy from 10⁶ eV to 10²¹ eV. Their energy spectra for many nuclei are known in detail from the measurements on the earth. To measure cosmic rays in the Galaxy, however, we need a chemical method using spectroscopy. H₃⁺ provides the ideal probe for this purpose because of (1) its ubiquity, (2) simple chemistry, and (3) concise spectrum. For about 30 years from the classic paper by Spitzer and TomaskoSpitzer, Jr, L. and Tomasko, H. G. 1968, ApJ, 152, 972(1968) when H⁺ was used as the probe, the cosmic ray ionization rate of H₂ was thought to be on the order of ζ  ∼  10⁻¹⁷ s⁻¹ and uniform throughout the Galaxy. The 1997 discovery of H₃⁺ in diffuse clouds and in the Galactic center (GC), however, changed this picture drastically. It is now established that ζ in diffuse clouds is 10 times higher than in dense cloudsIndriolo, N. and McCall, B. J. 2012, ApJ, 745, 91nd ζ in the Central Molecular Zone of the GC is 1000 times higherOka, T., Geballe, T. R., Goto, M., Usuda, T., McCall, B. J., and Indriolo, N. 2019, ApJ, submitted The uniformity of cosmic ray energy density throughout the Galaxy which was once thought to be reasonable because of its high penetrability has been negated. I will analyze these results using the Bethe formula for the cross section of ionization and discuss their implication in astrophysics and astrochemistry.

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Spitzer, Jr, L. and Tomasko, H. G. 1968, ApJ, 152, 972(1968), Indriolo, N. and McCall, B. J. 2012, ApJ, 745, 91a Oka, T., Geballe, T. R., Goto, M., Usuda, T., McCall, B. J., and Indriolo, N. 2019, ApJ, submitted.

The chemistry, and radiative and collisional interactions of H₃⁺ in the early Universe are examined. The object of study is to investigate whether H₃⁺ is essential in cooling of the primordial gas and thus in the formation of the first stars. The consensus so far is overwhelmingly negative. Most previous papers ignore the possibility at the onset because of the very low concentration of H₃⁺, about 10⁻⁹ of H₂ or less. Since the dipole infrared emission of H₃⁺ is (λ/a)²2  ∼  10⁹ (λ wavelength: a molecular size) times faster than the quadrupole emission of H₂, however, there is a possibility that H₃⁺ is comparably efficient coolant as H₂. Glover and SavinGlover, S. C. O. and Savin, D. W. 2009, MNRAS, 393, 911as the only paper which took this possibility into account. They negate the contribution of H₃⁺ because at a gas density higher than 10⁸ cm⁻³ H₃⁺ number density is further reduced by endothermic reaction H₃⁺ + H → H₂ + H₂⁺. We will examine this. We will consider the following two effects which have been neglected by the previous workers: (1) the effect of collision which convert translational energy of the gas into the energy of vibration and rotation of the molecules and (2) the effect of spontaneous emission between rotational levels. We find H₃⁺ can be a more efficient coolant than H₂ in the early Universe depending on temperature, density, and cosmological conditions of the primordial gas at the time of star formation.

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Glover, S. C. O. and Savin, D. W. 2009, MNRAS, 393, 911w

A custom-built multipass gas cell capable of supporting a high voltage electric discharge in situ was constructed and installed on the far infrared beamline at the Canadian Light Source (CLS). The 1.4 m cell can be aligned to achieve a total absorption pathlength of 24 m and when combined with a Bruker IFS12HR FTIR spectrometer (0.000959 cm⁻¹⁾ and synchrotron light, this new experiment is designed to collect high resolution infrared spectra of the complex mixture of molecular species generated in a high voltage (up to 3 kV) discharge. Preliminary tests have included CH₃NCS as a precursor to generate HNCS, a known astronomical species. The rich spectra recorded at the CLS include series of pure rotational transitions in the far IR region below 500 cm⁻¹ and rotationally resolved vibrational bands of which the strongest is the CN stretching mode at 1989 cm⁻¹. The ongoing analysis of the rovibrational spectrum of this highly fluxional molecule will be discussed. These preliminary studies lay the foundation for improved descriptions of the lowest energy states of floppy molecules and the far IR signatures needed to pursue their astronomical detection.

r0pt Figure Germane (GeH₄) is present in the atmospheres of the giant planets Jupiter and Saturn. Our recent analysis presented the complete modeling of line positions and intensities in the ν₁/ν₃ stretching dyad region near 2100 cm⁻¹V. Boudon et al. , J. Quant. Spectrosc. Radiat. Transfer 205, 174-183 (2018) of great interest for planetary applications. Nevertheless, this region contains a lot of hot bands. This situation leads to a very dense spectrum making deeper analyses difficult. In this study we present the first analysis and modeling of line positions in the ν₂/ν₄ bending dyad region for the five isotopologues. This analysis was conducted thanks to the formalism and programs developed in Dijon and allows to determine energy levels that are well suited for the hot band analyses, and therefore is a great improvement in the development of an accurate modeling needed for radiative transfer calculation for giant planets. These data will be integrated in our spectroscopic database (GeCaSDahttp://vamdc.icb.cnrs.fr/PHP/gecasda.php of calculated positions and intensities as soon as absolute intensities will be extracted from the spectra.

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V. Boudon et al. , J. Quant. Spectrosc. Radiat. Transfer 205, 174-183 (2018), http://vamdc.icb.cnrs.fr/PHP/gecasda.php)

The atomization energy of the ground electronic state of H₂O is determined with unprecedented precision. The story of how this was obtained, and about future possibilities, is presented.

We present the first variational calculation of a room temperature ab initio line list for the CH₃ radical. It is based on a high level ab initio potential energy surface and dipole moment surface of CH₃ in the ground electronic state. The ro-vibrational energy levels and Einstein A coefficients were calculated using the general-molecule variational approach implemented in the computer program TROVE. Vibrational energies and vibrational intensities are found to be in very good agreement with the available experimental data.

Numerous nitrile/isonitrile pairs have been detected in the interstellar medium; the isonitriles are suggested to be generated by nonthermal processes. Benzonitrile (C₆H₅CN) was recently detected in Taurus Molecular Cloud 1 (TMC-1) by radioastronomy. Herein, we report the analysis of benzoisonitrile (C₆H₅NC, μ_a = 4.0 D) ground vibrational state and its two lowest-energy vibrational states, ν₂₂ (141 cm⁻¹, calculated at the B3LYP/6-311+G(2d,p) level of theory) and ν₃₃ (155 cm⁻¹), in the 135 – 375 GHz frequency region. Over 4500 new rotational transitions have been measured in the ground vibrational state, main isotopologue. The rotational and distortion constants determined in this work may be used to search for benzoisonitrile in the interstellar medium. The Coriolis-coupled dyad reported herein, containing over 3000 new transitions for each vibrational state, has been analyzed for the first time, including resonances and several nominal interstate transitions, resulting in ∆E_22,33 = 9.682258(3) cm⁻¹and ζ^a_22,33 = 0.857780(1). Comparisons with the analogous states of benzonitrile are discussed.