The helium hydride ion, HeH⁺, is the simplest heteronuclear diatomic, and is composed of the two most abundant elements in the universe. It is widely believed that this ion was among the first molecules to be formed; thus it has been of great interest to scientists studying the chemistry of the early universe.¹² HeH⁺ is also isoelectronic to H₂ which makes it a great target ion for theorists to include adiabatic and non-adiabatic corrections to its Born-Oppenheimer potential energy surface. The accuracy of such calculations is further improved by incorporating electron relativistic and quantum electrodynamic effects.³
Using the highly sensitive spectroscopic technique of Noise Immune Cavity Enhanced Optical Heterodyne Velocity Modulation Spectroscopy (NICE-OHVMS) we are able to perform sub-Doppler spectroscopy on ions of interest. When combined with frequency calibration from an optical frequency comb we fit line centers with sub-MHz precision as has previously been shown for the H₃⁺, HCO⁺, and CH₅⁺ ions.⁴ Here we report a list of the most precisely measured rovibrational transitions of HeH⁺ to date. These measurements should allow theorists to continue to push the boundaries of ab initio calculations in order to further study this important fundamental species.
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¹S. Lepp, P. C. Stancil, A. Dalgarno J. Phys. B (2002), 35, R57. ²S. Lepp, Astrophys. Space Sci. (2003), 285, 737. ³K. Pachucki, J. Komasa, J. Chem. Phys (2012), 137, 204314. ⁴J. N. Hodges, A. J. Perry, P. A. Jenkins II, B. M. Siller, B. J. McCall J. Chem. Phys. (2013), 139, 164201.

According to the big bang theory, HeH⁺ was the first molecule ever produced in our universe, along with He₂⁺. It is also the simplest two-electron molecular system and lightest heteronuclear molecule, with a stable ground electronic state, aside from the isotopologues of H₂. These facts make HeH⁺ very interesting for experimental studies of the early universe and theoretical studies of isotope effects including Born-Oppenheimer breakdown (BOB), as well as an extremely important benchmark system for ab initio methods. However, no spectroscopic measurements, nor ab initio calculations have been reported for HeT⁺, and the most accurate empirical potentials for HeH⁺ and HeD⁺ are 15 years old and are unreliable outside of the data range. We build the most accurate analytical empirical potentials and BOB functions for HeH⁺ and HeD⁺ to date. These BOB functions are then used to predict the HeT⁺ potential, and are in excellent agreement with our ab initio potential for HeT⁺. Outside the data-range, the MLR (Morse/long-range) model forces the analytic empirical potential to become the theoretically correct long-range potential based on the multipole polarizabilties of He. We include the dipole and quadrupole polarizabilities. The quadrupole value includes finite-mass and relativistic corrections, and an estimate of the leading α³ QED corrections. The dipole value includes finite-mass, relativistic, and QED corrections up to the leading term of the α⁴ effects.

Being the simplest neutral open shell molecule, BeH is a very important benchmark system for ab initio calculations. However, the most accurate empirical potentials and Born-Oppenheimer breakdown (BOB) functions for this system are nearly a decade old and are not reliable in the long-range region. Particularly, the uncertainties in their dissociation energies were about ±200 cm⁻¹, and even the number of vibrational levels predicted was at the time very questionable, meaning that no good benchmark exists for ab initio calculations on neutral open shell molecules. We build new empirical potentials for BeH, BeD, and BeT that are much more reliable in the long-range. Being the second lightest heteronuclear molecule with a stable ground electronic state, BeH is also very important for the study of isotope effects, such as BOB. We extensively study isotope effects in this system, and we show that the empirical BOB functions fitted from the data of any two isotopologues, is sufficient to predict crucial properties of the third isotopologue.

Electronic contributions to molecular properties are often considered as the major factor and usually reported in the literature without ro-vibrational corrections. However, there are many cases where the nuclear motion contributions are significant and even larger than the electronic contribution. In order to obtain accurate theoretical predictions, nuclear motion effects on molecular properties need to be taken into account. The computed isotropic hyperfine coupling constants for the nonvibrating methyl radical CH₃ are far from the experimental values. For CH₃, we have calculated the vibrational-state-dependence of the isotropic hyperfine coupling constant in the electronic ground state. The vibrational wavefunctions used in the averaging procedure were obtained variationally with the TROVE program. Analytical representations for the potential energy surfaces and the hyperfine coupling constant surfaces are obtained in least-squares fitting procedures. Thermal averaging has been carried out for molecules in thermal equilibrium, i.e., with Boltzmann-distributed populations. The calculation methods and the results will be discussed in detail.

Although the torsional spectrum of several isotopic species of methanol with a symmetrical CH₃ or CD₃ was analyzed some time ago, it is recently,¹ and only for the monodeuterated species CH₂DOH, that such an analysis was extended to the case of an asymmetrical methyl group. In this talk, based on a Fourier transform high-resolution spectrum recorded in the 20 to 670 cm⁻¹ region, the first analysis of the torsional spectrum of doubly deuterated methanol CHD₂OH will be presented. The Q branch of many torsional subbands could be observed and their assignment was initiated using a theoretical torsion-rotation spectrum computed with an approach accounting for the torsion-rotation Coriolis coupling and for the dependence of the generalized inertia tensor on the angle of internal rotation.² 46 torsional subbands were thus assigned. For 28 of them, their rotational structure could be assigned and fitted using an effective Hamiltonian expressed as a J(J+1) expansion; and for 2 of them microwave transitions within the lower torsional level could also be included in the analysis.³ In several cases these analysis revealed that the torsional levels are strongly perturbed.⁴ In the talk, the torsional parameters retrieved in the analysis of the torsional subband centers will be discussed. The results of the analysis of the rotational structure of the torsional subbands will be presented and we will also try to understand the nature of the perturbations. At last, preliminary results about the analysis of the microwave spectrum will be presented.
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¹El Hilali, Coudert, Konov, and Klee, J. Chem. Phys. 135 (2011) 194309 ²Lauvergnat, Coudert, Klee, and Smirnov, J. Mol. Spectrosc. 256 (2009) 204 ³Quade, Liu, Mukhopadhyay, and Su, J. Mol. Spectrosc. 192 (1998) 378 ⁴Pearson, Yu, and Drouin, J. Mol. Spectrosc. 280 (2012) 119

Acetamide is an oblate asymmetric top displaying almost free internal rotation of its methyl group. The microwave spectrum of the normal species (CH₃C(=O)NH₂) has already been studied and a value¹ of only 25 cm⁻¹ was retrieved for the height of the potential barrier hindering the internal rotation. No spectroscopic results are available about the monodeutared species with a partially deuterated CH₂D methyl group which will be the subject of the present talk. The effects of deuteration on the hindering potential² will be investigated first. They lead to qualitative changes of the hindering potential no longer resembling that of the normal species and displaying several inequivalent minima.³ A determination of the torsional potential will be attempted through an analysis of the microwave spectrum of the monodeuterated species in which torsion-rotation energies are calculated with the approach developed for monodeuterated methanol,⁴ accounting for the torsion-rotation Coriolis coupling and for the dependence of the inertia tensor on the torsional angle. A low temperature spectrum, recorded with the MB-FTMW spectrometer in Lille, has already been analyzed and 14 transitions could be assigned up to J=6. Room temperature spectra have also been recorded in the 7-91 and 150-165 GHz frequency ranges and more than 100 transitions have been assigned up to J=16 for the ground torsional state. In the paper, deuteration effects will be discussed and we hope to assign a sufficient number of microwave transitions in order to obtain the first quantitative information about the hindering potential of monodeuterated acetamide.
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¹Ilyushin, Alekseev, Dyubko, Kleiner, and Hougen, J. Molec. Spectrosc. 227 (2004) 115 ²Lauvergnat, Coudert, Klee, and Smirnov, J. Molec. Spectrosc. 256 (2009) 204 ³Margulès, Coudert, Møllendal, Guillemin, Huet and Janeckovà, J. Molec. Spectrosc. 254 (2009) 55 ⁴Coudert, Zemouli, Motiyenko, Margulès, and Klee, J. Chem. Phys. 140 (2014) 064307

This study follows our recent investigations about deuterated methyl-top species of complex organic molecules: methanol,¹ methyl formate,² and dimethyl ether.³ In particular these works led the first ISM detection of HCOOCH₂D and CH₂DOCH₃. Acetaldehyde is not very abundant in the ISM, but this is a very interesting case from the spectroscopic point of view as it is an intermediate case between methyl formate and methanol. In the normal species of acetaldehyde, the barrier to internal rotation⁴ V₃ is 408cm⁻¹ which is close to the value in methyl formate⁵: 373 cm⁻¹. However, the value of the Coriolis coupling constant ρ is 0.33 in acetaldehyde which is a much larger value than in methyl formate, 0.08, meaning that the coupling between the torsion and the overall rotation is more important.
The sample was not a commercial one and half of its amount is the normal species which leads to a more difficult line assignment. The spectra were recorded in Lille between 75 and 950 GHz with a solid-state submillimeter-wave spectrometer. The starting point of the analysis was the centimeter-wave measurements carried out for the sym and asym- conformers.⁶ A comparison between the approach developed for deuterated methyl formate (HCOOCH₂D), based on the water dimer formalism, and that designed recently for deuterated methanol^a (CH₂DOH) will be presented.
This work is supported by the CNES and the Action sur Projets de l'INSU, PCMI.
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¹Coudert, L. H.; et al. J. Chem. Phys. 140, (2014) 64307 ²Coudert, L. H.; et al. ApJ 779, (2013) 119 ³Richard, C.; et al. A&A 552, (2013) A117 ⁴Smirnov, I. A.; et al. J. Mol. Spectrosc.  295 (2014) 44 ⁵Ilyushin, V.; et al. J. Mol. Spectrosc.  255 (2009) 32 ⁶Turner, P. H.; and Cox, A. P. Chem. Phys. Lett. 42, (1976) 84 - Turner, P. H.; Cox, A. P.; and Hardy, J. A. J.C.S. Farady Trans. 2, (1981) 1217

PAHs molecules and derivatives have long been suspected to be present in different objects of the universe but no unambiguous detection (based on rotationally resolved spectroscopy) has been reported yet. Pure rotation transitions in the ground state (GS) of quinoline (which belongs to the C_s point group) have been analyzed in a previous work of Kisiel et al.¹ using micro-wave and sub-mm techniques. We will present in this talk a collective effort to record and assign the rotational structure of the two lowest vibrational states of quinoline (namely ν₄₅ and ν₄₄ centered at about 168.5 cm⁻¹ and 177.6 cm⁻¹ respectively). In this study, high resolution synchrotron based FT-FIR together with pure rotation spectroscopy in the sub-mm range permitted to obtain very complementary data. The spectral analysis permitted to identify relatively large perturbation patterns across a K_a difference of 2 between the two excited states (both states are A" symmetry). Successful treatment of the perturbations allowed for the accurate determination of i) the rotational constants in the excited states ii) the Fermi and Coriolis perturbation terms and iii) the relative energies of ν₄₅ and ν₄₄ to the GS. Since most of the PAHs molecules possess low frequency out of plane vibrations which are relatively close in energy, this study emphasizes the difficulties encountered to simulate accurately the rotational structures of such large molecules in excited vibrational states.
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¹Z. Kisiel, O. Desyatnyk, L. Pszczolkowski, S. B. Charnley and P. Ehrenfreund, J. Mol. Spectrosc. 217, 115 (2003)

Due to their role in determining the intensities of rotational transitions, accurate dipole moments are an important resource for evaluating the prospects of observing a candidate astromolecule. We have used high level ab initio calculations [mostly RCCSD(T) with aug-cc-pVQZ basis sets] to calculate the equilibrium dipole moments and dipole polarizabilities of nearly 80 compounds with up 6 atoms that contain silicon or phosphorus. To date, 17 observed astromolecules contain these elements, and more detections are likely as experimental data for their rotational transitions becomes available for interpreting observations from ALMA and other telescopes. We will compare the results from RCCSD(T) with other methods, including B3LYP and MP2. We will also describe the basis set dependence of our results, which varies considerably within the set of Si- and P-containing compounds we have studied.

We report eight new ultra-high precision (±5 kHz) measurements of purely rotational N(1←0) transitions in several vibrational states of all stable isotopologues of the ground X(1¹Σ⁺) -state of ZnO. Combined with previous high-resolution (±50 kHz) measurements of purely rotational transitions between higher rotational states for the same system¹, we are able to build analytic potentials for ⁶⁴Zn¹⁶O, ⁶⁶Zn¹⁶O, ⁶⁷Zn¹⁶O, ⁶⁸Zn¹⁶O, and ⁷⁰Zn¹⁶O, that are in full agreement with all known spectroscopic measurements of the system. Despite there being absolutely no vibrational information, our empirical potentials are able to determine the size of the vibrational spacings and the bond lengths, each with a precision of more than two orders of magnitude greater than the most precise empirical values previously known. We then use the XDM method to calculate values for the C₆, C₈, and C₁₀ long-range constants for this molecule, and use these to accurately anchor the long-range regions of the potentials, where no measurements have yet been performed. In the region lying between the short-range measurements and the long-range theory on which our potentials are based, our final analytic global potentials are in very good agreement with state of the art ab initio potentials.
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¹L. N. Zack, R. L. Pulliam, L. M. Ziurys, J. Mol. Spec., 256, 186-191 (2009).