Over the past years a new infrastructure for atomic and molecular databases has been developed within the framework of the Virtual Atomic and Molecular Data Centre (VAMDC). Standards for the representation of atomic and molecular data as well as a set of protocols have been established which allow now to retrieve data from various databases through one portal and to combine the data easily. Apart from spectroscopic databases such as the Cologne Database for Molecular Spectroscopy (CDMS), the Jet Propulsion Laboratory microwave, millimeter and submillimeter spectral line catalogue (JPL) and the HITRAN database, various databases on molecular collisions (BASECOL, KIDA) and reactions (UMIST) are connected. Together with other groups within the VAMDC consortium we are working on common user tools to simplify the access for new customers and to tailor data requests for users with specified needs. This comprises in particular tools to support the analysis of complex observational data obtained with the ALMA telescope. In this presentation requests to CDMS and JPL will be used to explain the basic concepts and the tools which are provided by VAMDC. In addition a new portal to CDMS will be presented which has a number of new features, in particular meaningful quantum numbers, references linked to data points, access to state energies and improved documentation. Fit files are accessible for download and queries to other databases are possible.

Composite potential energy surfaces with coupled-cluster contributions up to CCSDTQP were constructed for C₃ and l-C₃H⁺ and used in the calculation of spectroscopic properties. The use of very large AO basis sets and the consideration of higher-order correlation beyond CCSD(T) is of utmost importance for C₃ in order to arrive at quantitative spectroscopic data. The first detection of l-C₃H⁺ in the interstellar medium was reported by Pety et al.,¹ who attributed 9 radio lines observed in the horsehead photodissociation region to that species. That assignment was questioned by the recent theoretical work of Huang et al.² However, our more accurate calculations are well in support of the original assignment. The calculated ground-state rotational constant is B₀ = 11248 MHz, only 0.03% off from the radio astronomical value of 11244.9512±0.0015 MHz. The ratio of centrifugal distortion constants D₀(exp.)/D_e(theor.) of 1.8 is quite large, but reasonable in comparison with C₃O³ and C₃.
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¹J. Pety, P. Gratier, V. Guzmán, E. Roueff, M. Gerin et al., Astron. Astrophys. 2012, A68, 1-8. ²X. Huang, R. C. Fortenberry, T. J. Lee, Astrophys. J. Lett. 2013, 768:L25, 1-5. ³P. Botschwina, R. Oswald, J. Chem. Phys. 2008, 129, 044305.

Terahertz absorption spectroscopy was employed to detect the ground-state inversion transitions of the hydronium ion. The highly excited ions were created with an extended negative glow discharge through a gas mixture of 1 mtorr of H₂O, 2 mtorr of H₂, and 12 mtorr of Ar, which allowed observation of transitions with J and K up to 12. In total forty seven transitions were measured in the 0.9-2.0 THz region and twenty two of them were observed for the first time. The experimental uncertainties range from 100 to 300 kHz, which are much better than those of 0.3-1.2 MHz reported in previous work. Differences up to 25.6 MHz were found between the observed positions and the catalog values that have been used for Herschel data analysis of observations towards Sagittarius B2(N), NGC 4418 and Arp 220.¹² The new and improved measurements were fit to experimental accuracies with an updated Hamiltonian; and better H₃O⁺ predictions are reported to support the proper analysis of astronomical observations by high-resolution spectroscopy telescopes, such as Herschel,³ SOFIA, and ALMA.
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¹Lis et al., Hot, metastable hydronium ion in the Galactic center: formation pumping in X-ray-irradiated gas? , Phil. Trans. R. Soc. A 370, 5162 (2012). ²González-Alfonso et al., Excited OH⁺, H₂O⁺ and H₃O⁺ in NGC 4418 and Arp 220 , Astrophys. Astronom 550, A25 (2013). ³Lis et al., Widespread rotaional-hot hydronium in the Galactic Interstellar Medium , Astrophys. J., submitted (2014).

Ethyl cyanide, CH₃CH₂CN, is a highly abundant molecule in hot cores associated with massive star formation where temperatures often approach 200 K. 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 v₂₀ and v₁₂ vibrational states^a, many aspects of the spectroscopy of the v₂₀ state are not adequately characterized. Torsional splittings in the b-type spectrum of v₂₀ 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 v₂₀ are 2v₂₁, 2v₁₃ and v₂₁ + v₁₃. It has been determined that v₂₀ interacts weakly with both 2v₂₁ and 2v₁₃ and that 2v₂₁ interacts weakly with 2v₁₃, in spite of their common symmetry and very close proximity. However, all the interactions of v₂₁ + v₁₃ 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. We present what is known and unknown in this quartet of CH₃CH₂CN states. ^aDaly, A. M., Bermúdez, C., López, A., et al., 768, 1, ApJ, 2013

The identification of a large variety of chemical compounds in space as well as planetary atmospheres has been made possible through the spectral signatures of astronomical bodies. For their interpretation, laboratory measurements are essential and rotational spectroscopy plays a leading role. Recent missions, such as the Herschel Space Observatory and the Stratospheric Observatory for Infrared Astronomy (SOFIA), have pointed out the need for precise and accurate frequency measurements and spectroscopic parameters in the submillimeter-wave range. The higher spectral resolution that can be exploited by the Atacama Large Millimeter Array (ALMA) is expected to play a key role in the detection of complex species as well as rare isotopologues. In the present contribution, the millimeter-/submillimeter-wave spectrometer working at the University of Bologna and its applications in the field of astronomical observations are presented. The focus is here on the accuracy of the retrieved transition frequencies of neutral as well as ionic species.

We have studied methanol, one of the so-called ‘astronomical weeds’, in the 215-265 GHz band. We have gathered a set of intensity calibrated, complete, experimental, and temperature resolved spectra from across the temperature range of 240-389 K. A number of low lying transitions, including the ν_t = 3 , have not been produced by available catalogs. Using our previously reported method of analysis¹ we were able generate a line list that contains lower state energies and linestrengths, for all of the observed lines in the band. This line list includes those lines which have no quantum mechanical assignment. In addition to this line list we provide a point by point method capable of generating the complete spectrum at an arbitrary temperature. The sensitivity of the point by point analysis is such that we are able to identify lines which would not have manifest in a single scan across the band. The consequence has been to reveal not only a number of new methanol lines, but also trace amounts of contaminants. We show how the intensities from the contaminants can be removed with indiscernible impact on the signal from methanol. To do this we use the point by point results from our previous studies of these contaminants. The efficacy of this process serves as strong proof of concept for usage of our point by point results on the problem of the weeds. The success of this approach for dealing with the weeds has also previously been reported².
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¹S. Fortman et al. 2014 ApJ 782 75 ²S. Fortman et al. 2012 J. Mol. Spectrosc. 782, 75

Acetonitrile (CH₃CN) is a well-known interstellar molecule whose vibrationally excited states need to be accounted for in searches for new molecules in the interstellar medium. To help catalog such `weed' molecules, we have developed a technique that involves recording complete spectra over a range of astrophysically significant temperatures. With such a data set, we can experimentally measure the line strengths and lower state energies of unassigned lines in the spectrum. In this talk we will present the ongoing analysis of complete temperature resolved spectra in the 215-265 GHz and 570-650 GHz regions. We have been able to assign many vibrationally hot lines from this data and a room temperature data set spanning 165-700 GHz. To date, we have assigned lines from most of the vibrational states below ν₆ at 1448 cm⁻¹.

The detection of propenal (acrolein) in Sgr B2 is based in two transitions detected with the Green-Bank Telescope,¹ operating in the frequency range 18-26 GHz. A combination of Stark modulated microwave spectroscopy and frequency modulated millimeter- and submillimeter-wave spectroscopy has been used to record the rotational spectrum of propenal from 26 to 675 GHz in order to provide accurate rotational parameters for the identification of new lines of propenal in the interstellar medium. Ground state and the vibrational excited states below 700 cm⁻¹ of trans-propenal (ν₁₈, 2ν₁₈, ν₁₃, 3ν₁₈, ν₁₈+ν₁₃, ν₁₂, ν₁₇, 4ν₁₈, 2ν₁₈+ν₁₃, 2ν₁₃) have been analyzed in a global fit taking in to account Coriolis and Fermi interactions. Spectroscopic constants for all three ¹³C trans-isotopologes in natural abundance as well as ground state spectroscopic constants for cis-propenal are also reported.
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¹J. M. Hollis, P. R. Jewell, F. J. Lovas, A. Remijan, H. Møllendal Astrophys. J. 610, L21-L24, (2010)

The torsional spectrum of C₂H₆ has been investigated from 220 to 330 cm⁻¹ to measure the intensity of the fundamental and the first torsional hot band needed for atmospheric studies of Titan. Several spectra were measured at resolutions of 0.01 and 0.02 cm⁻¹ using the JPL Bruker IFS-125 coupled to a coolable multi-pass absorption cell originally developed at University of British Columbia.¹ Spectra were recorded at several temperatures from 293 K to 166 K, with the lower temperatures relevant to the stratosphere of Titan. Because this spectrum is very weak, a long absorption path of 52 m was used along with substantial sample pressures from 35 to 255 Torr. Intensities were analysed using a quantum mechanical model reported previously.² The torsional fundamental of C₂H₆ is observed in the CIRS spectra of Titan. Line parameters for the torsional bands are required for accurate characterization of spectral features of Titan’s far-infrared region. The current study should lead to a better understanding of the methane cycle in planetary atmospheres and permit the identification of the other molecular features in the CIRS data.³
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¹E. H. Wishnow, A. Leung, and H. P. Gush, Rev. Sci. Instr., 70, 23 (1999). ²N. Moazzen-Ahmadi, A.R.W. McKellar, J.W.C. Johns, and I.Ozier, J. Chem. Phys. 97, 3981 (1992). ³Research described in this paper was performed, in part, at the Jet Propulsion Laboratory, California Institute of Technology under contracts and cooperative agreements with the NASA.The data were obtained using NASA’s OPR Grant awarded to the College of William and Mary. The research conducted at the University of Calgary is supported by the Canadian Space Agency.

Photodissociation of ¹⁴N₂ and ¹⁴N ¹⁵N occurs in interstellar clouds, protoplanetary discs, (exo)planetary atmospheres, and other environments due to ultraviolet radiation originating from stellar sources and the presence of cosmic rays. We study this process in detail in search of an explanation for the observed non-elemental ratios of N isotopologues observed in solar system bodies and in molecular clouds. High-resolution theoretical photodissociation cross sections of N₂ and competing UV-absorbing species are used to calculate the isotope-selective shielding of N₂ in photochemical models of a diffuse interstellar cloud and protoplanetary disk. An enhancement of the atomic ¹⁵N/¹⁴N ratio over the elemental value is obtained due to the self-shielding of external radiation at an extinction of about A_v=1 mag, and leads to a similar mass fractionation in daughter species. This effect is larger where assumed grain growth has reduced the opacity of dust to ultraviolet radiation. The cosmic-ray induced dissociation of N₂ is calculated from a high-resolution model of H₂ emission and is found to depend sensitively on details of the emission and photodissociation cross sections.

Polycyclic aromatic hydrocarbons (PAHs), in particular, their radical cation (PAH⁺), have long been postulated to be the important molecular species in connection with the spectroscopic observations¹ in the interstellar medium. Motivated by numerous important observations by stellar as well as laboratory spectroscopists, we undertook detailed quantum mechanical studies of the structure and dynamics of electronically excited PAH⁺ in an attempt to establish possible synergism with the recorded data². In this study, we focus on the quantum chemistry and dynamics of the doublet ground (X) and low-lying excited (A, B and C) electronic states of the radical cation of tetracene (Tn), pentacene (Pn), and hexacene (Hn) molecule. This study is aimed to unravel photostability, spectroscopy, and time-dependent dynamics of their excited electronic states. In order to proceed with the theoretical investigations, we construct suitable multistate and multimode Hamiltonian for these systems with the aid of extensive ab initio calculations of their electronic energy surfaces. The diabatic coupling surfaces are derived from the calculated adiabatic electronic energies. First principles nuclear dynamics calculations are then carried out employing the constructed Hamiltonians and with the aid of time-independent and time-dependent quantum mechanical methods³. We compared our theoretical results with available photoelectron spectroscopy, zero kinetic energy photoelectron (ZEKE) spectroscopy and matrix isolation spectroscopy (MIS) results. A peak at 8650 Å in the B state spectrum of Tn⁺ is in good agreement with the DIB at 8648 Å observed by Salama et al. Similarly in Pn⁺, a peak at 8350 Å can be correlated to the DIB at 8321 Å observed by Salama et al.
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¹J. Zhang et al., J. Chem. Phys., 128,104301 (2008).; F. Salama, Origins of Life Evol. Biosphere, 28, 349 (1998).; F. Salama et al., Planet. Space Sci., 43, 1165 (1995).; F. Salama et al., Astrophys. J., 526, 265 (1999).; J. Szczepanski et al., Chem. Phys. Lett., 232, 221 (1995).; J. Szczepanskiet al., Chem. Phys. Lett., 245, 539 (1995).; J. Zhang et al., Astrophys. J., 715, 485 (2010). ²V. Sivaranjana Reddy et al., Phys. Rev. Lett, 104, 111102 (2010).; S. Ghanta et al., Phys. Chem. Chem. Phys. 13, 14523.; & 13, 14531 (2011). ³S. Nagaprasad Reddy et al., J. Phys. Chem. A., 117, 8737 (2013).