The Fourier Transform infrared spectra of CH₃NO₂, have been recorded, in the 400-950 cm⁻¹spectral region, at a resolution of 0.00096 cm⁻¹, using the Far-Infrared Beamline at Canadian Light Source. The observed spectra contain four fundamental vibrations: the NO₂ in-plane rock (475.2 cm⁻¹), the NO₂ out-of-plane rock (604.9 cm⁻¹), the NO₂ symmetric bend (657.1 cm⁻¹), and the CN-stretch (917.2 cm⁻¹). For the lowest torsional state of CN-stretch and NO₂ in-plane rock, transitions involving quantum numbers, m" = 0; J" ≤ 50 and K_a^" ≤ 10, have been assigned with the aid of an automated ground state combination difference program together with a traditional Loomis Wood approach¹. Ground state combination differences derived from more than 2100 infrared transitions have been fit with the six-fold torsion-rotation program developed by Ilyushin et.al². Additional sextic and octic centrifugal distortion parameters are derived for the ground vibrational state.
-----
¹C. F. Neese., An Interactive Loomis-Wood Package, V2.0, 56^th,OSU Interanational Symposium on Molecular Spectroscopy (2001). ²V. V. Ilyushin, Z. Kisiel, L. Pszczolkowski, H. Mader, and J. T. Hougen, J. Mol. Spectrosc. 259, 26, (2010).

The high-resolution rotationally resolved Fourier Transform Far-infrared spectrum of the NO₂ in plane-rock band (440-510 cm⁻¹) of nitromethane (CH₃NO₂) has been recorded using the Far-Infrared Beamline at the Canadian Light Source, with a resolution of 0.00096 cm⁻¹. More than 1500 transitions lines have been assigned for m′ = 0; K_a^′ ≤ 7; J^′ ≤ 50; using an automated ground state combination difference program together with the traditional Loomis Wood approach¹. Transitions involving m′ = 0; K_a^′ ≤ 7; J′ ≤ 20; in the upper vibrational state are fit using the six-fold torsion-rotation program developed by Ilyushin et.al². The torsion-rotation energy pattern in the lowest torsional state ( m′ = 0) of the upper vibrational state is similar to that of the vibrational ground state.
-----
¹C. F. Neese., An Interactive Loomis-Wood Package, V2.0, 56^th,OSU Interanational Symposium on Molecular Spectroscopy (2001). ²V. V. Ilyushin, Z. Kisiel, L. Pszczolkowski, H. Mader, and J. T. Hougen, M. Mol. Spectrosc. 259, 26, (2010).

The barrier to methyl internal rotation of an asymmetric two ring system depends on the position of the methyl substitution. A cavity based Fourier transform microwave spectrometer was used to record rotational spectra of different methyl substituted indoles in the range of 10.5 - 20 GHz. About 160 hyperfine components arising from about 30 rotational transitions were assigned for each 1- and 3-methylindole. The program XIAM^a was used to fit the rotational constants, distortion constants, nuclear quadrupole coupling constants and barrier to internal rotation to the measured transition frequencies of the A and E internal rotation states.
The best fit values for the rotational constants are A = 2651.12(2) MHz, B = 1305.266(2) MHz, C = 879.800(2) MHz for 1-methylindole and A = 2603.7224(5) MHz, B = 1268.7886(1) MHz, C = 857.8091(1) MHz for 3-methylindole. The different values observed for the barrier to internal rotation, 279.8(3) cm⁻¹for 1-methylindole and 433(1) cm⁻¹for 3-methylindole, may be due to the different rotor axis lengths and differences in local π-electron density.
Progress on the assignment of additional methylated indoles will also be presented.
^aH. Hartwig and H. Dreizler, Z. Naturforsch, 51a, 923 - 932.

We present the rotational spectra studies of two acetamide conjugated molecules, namely, N-methylformamide (CH₃NHCHO) and propionamide (CH₃CH₂CONH₂). New measurements have been performed in the frequency range 50 - 150 GHz using the spectrometer in Kharkov, and in the frequency range 150 - 630 GHz using the spectrometer in Lille. The analysis of the rotational spectra of both molecules is complicated by the methyl top internal rotation and nuclear quadrupole hyperfine structure. In case of N-methylformamide the barrier to internal rotation is relatively small, V₃ = 51.7 cm⁻¹, whereas for propionamide the barrier is high, V₃ = 751.9 cm⁻¹. For propionamide the presence of the low-lying excited vibrational state (60 cm⁻¹) makes difficult the analysis within the classical rho-axis method Hamiltonian. In this case only the rotational transitions with K_a < 10 could be fitted within experimental accuracy. The rotational spectra of both molecules were analyzed using modified version of the RAM36 code, taking nuclear quadrupole hyperfine coupling into account. Details of the new study and problems encountered in the analysis will be discussed.

Recent discovery of methyl acetate in Orion KL¹ places the vinyl acetate as a potential candidate possibly present in the interstellar medium. The room-temperature rotational spectrum of vinyl acetate has been measured from 125 up to 360 GHz to provide direct frequencies to the astronomical community. Transition lines, corresponding to the most stable conformer, have been observed and assigned on the basis of the previously determined spectroscopic constants.² All the rotational transitions reveal the A−E splitting due to the methyl internal rotation and the precise set of the spectroscopic constants obtained from the least-squares fit to a threefold barrier internal rotation Hamiltonian is reported. Additional measurements have been also made using a broadband CP-FTMW spectrometer in the region of 6–18 GHz which made possible to assign all monosubstituted ¹³C and ¹⁸O isotopic species in natural abundance and to derive the molecular structure.
-----
¹B. Tercero, I. Kleiner, J. Cernicharo, H. V. L. Nguyen, A. López, and G. M. Muñoz Caro, Astrophys. J. Lett. 2013, 770, 13. ²B. Velino, A. Maris, S. Melandri, W. Caminati, J. Mol. Specrosc. 2009, 256, 228.

Graphical displays of C-H stretching normal-mode coefficients from recent quantum chemical projected-frequency calculations are compared with analogous displays constructed after reexamination of results from more extensive higher-level calculations described earlier in the literature. Such comparisons confirm the facts that: (i) no geometrical phase is accumulated in these coefficients when the methyl top undergoes one complete internal-rotation revolution with respect to the frame, and (ii) some of the coefficients, when plotted against the internal rotation angle, exhibit near-cusp-like behavior at one or two angles. The connection between these graphical displays and the magnitude of “Jahn-Teller-like” and “Renner-Teller-like” torsion-vibration interaction terms in a previously reported model Hamiltonian, as well as the connection between the lack of geometric-phase accumulation in these graphs and the number of conical intersections enclosed by one full internal-rotation motion, will also be briefly discussed.

The tert-Butyl acetate molecule was studied using a combination of quantum chemical calculations and molecular beam Fourier transform microwave spectroscopy in the 9 to 14 GHz range. Due to its rather rigid frame, the molecule possesses only two different conformers: one of C_s and one of C₁ symmetry. According to ab initio calculations, the C_s conformer is 46 kJ/mol lower in energy and is the one observed in the supersonic jet. We report on the structure and dynamics of the most abundant conformer of tert-butyl acetate, with accurate rotational and centrifugal distortion constants. Additionally, the barrier to internal rotation of the acetyl methyl group was determined. Splittings due to the internal rotation of the methyl group of up to 1.3 GHz were observed in the spectrum. Using the programs XIAM and BELGI-Cs, we determine the barrier height to be about 113 cm⁻¹ and compare the molecular parameters obtained from these two codes. Additionally, the experimental rotational constants were used to validate numerous quantum chemical calculations. This study is part of a larger project which aims at determining the lowest energy conformers of organic esters and ketones which are of interest for flavor or perfume synthetic applications¹.
-----
¹Project partly supported by the PHC PROCOPE 25059YB

The couplings between the CH stretch and CH₃ torsion in the methyl rotor have been widely studied in methanol.¹ In this research, we are focusing on the effect of this coupling on the vibrational spectrum in the CH stretch region of the methanol cation - argon cluster, CH₃OH⁺·Ar, and the methyl peroxy radical, CH₃OO·. A reduced dimensional analysis including the three CH stretches and the CH₃ torsion is used to calculate the spectra. The CH stretches are treated as harmonic oscillators whose frequency depends on the torsional angle because of coupling between the CH stretch and CH₃ torsion. The infrared spectrum of CH₃OH⁺·Ar cluster taken by the Duncan group² shows multiple peak structure in the CH stretch region. In this system, the calculation indicates the coupling between the CH₃ torsion and CH stretch is relatively strong. The multiple peak structure in the experimental spectrum can be assigned to the CH stretch fundamentals and the combination band involving the CH stretch and the CH₃ torsion. However, for the methyl peroxy radical, the calculated coupling is very weak. In the CH stretch region of the infrared spectrum of CH₃OO· taken by the Lee group³, only CH stretch fundamentals with relatively broad rotational contours are observed. The broadened structure of the CH stretch fundamental is possibly caused by sequence band structure from low lying torsional levels which are well populated and shift very little from the origin band.
-----
¹D. S. Perry J. Mol. Spectpsc. 2009, 257, 1-10 ²J. D. Mosley, J. W. Young, M. A. Duncan 68th International Symosium of Molecular Spectroscopy ³K.-H. Hsu, Y.-P. Lee, M. Huang, T. A. Miller 68th International Symosium of Molecular Spectroscopy

Rotationally-resolved vibrational spectra have been collected from 100-1000 cm⁻¹ for the four-membered ring trimethylene sulfide (c-C₃H₆S) using synchrotron light at the far infrared beamline of the Canadian Light Source. The spectra are complicated by the presence of ring inversion tunneling which gives rise to dense patterns of overlapping rotation-vibration-inversion transitions in the infrared region. These are well-resolved using the Bruker IFS125HR instrument. In this talk, we will discuss the progress of the analysis of the two lowest frequency bands which correspond to the c-type ring puckering vibration at 139 cm⁻¹, and the a-type in-plane ring deformation at 529 cm⁻¹. The ideas of genetic evolution via evolutionary strategies have been used to aid in the analysis of the observed spectra. In particular, we have applied the covariance matrix adaptation evolution strategy which uses the concept of mutation and the results of previous trials to give solutions to fit the quite dense spectra.

Rotationally-resolved direct infrared absorption spectra of hydroxymethyl radical (H₂COH) in the CH₂ asymmetric mode (ν₂) were observed for the first time using the Boulder difference frequency generation infrared spectrometer. Hydroxymethyl radical was formed with chemical selectivity via the reaction of Cl radical with CH₃OH in a discharge slit-jet supersonic expansion. As a result of sub-Doppler linewidth and low rotational temperature, the b-type rotational structure and spin-rotation splitting were fully resolved. In particular, tunneling splitting was observed due to the large-amplitude COH torsional mode. Because of the feasible permutation of hydrogens in the methylenic group, nuclear spin intensity alternation was given as: 3:1 for K_a=even, odd in the 0⁺ level, and 1:3 for K_a=even, odd in the 0⁻ level of the ground vibrational state. The assignments were confirmed rigorously by four-line ground state combination differences, which agreed within the experimental frequency uncertainty (10 MHz). The identified transitions were fit with a Watson A-reduction Hamiltonian including the spin rotational interaction, leading to unambiguous determination of asymmetric top spectroscopic constants, as well as spin rotational constants (ϵ_aa, ϵ_bb, ϵ_cc) for the first time.

Metal ions play important roles in biologically processes. Among these, alkali metal ions are of great importance. Their solvation is one of the fundamental processes having great effect on their activity and has been in focus of research for many years. M⁺H₂O cluster are a good model for microscopic solvation. However, modeling gas-phase cluster ions has been a challenge both experimentally and theoretically due to uncertainties in the temperature (or internal energy) of these species. The temperature depends primarily on the composition and method of preparation of the cluster ion. Infrared photodissociation spectroscopy in combination with argon tagging is a well suited tool to study these species. While argon tagging itself is a well established technique for lowering the temperature and sharpening spectral features, experiments with multiple attached Ar atoms are rare. The influence of up to three Ar atoms on cluster temperature, vibrational band origins and rotational constants will be discussed for M = Na, K, Rb and Cs. The structure, arising from rotation of the water subunit, of the asymmetric bands will be analyzed in detail. Many spectra show broadening/splitting of features and an unusual intensity distribution for features associated especially to transitions involving the |K|=1 level. The influence of a low barrier, hindering rotation of the water subunit within the cluster, will be discussed.

Hydroxymethyl radical (CH₂OH) is an important radical in modeling combustion flame chemistry as well as chemistry in the interstellar medium. We have recently observed high resolution jet cooled infrared spectra of CH₂OH, which reveal a rich pattern of splittings due to large-amplitude torsional tunneling of the COH moiety with respect to the methylenic framework. In order to facilitate a detailed analysis of these tunneling splittings, we have pursued high level ab initio CCSD(T) calculations of the multidimensional torsional tunneling potential energy surface using a MOLPRO package with correlated cc-pvnz-f12 basis sets and extrapolated to the complete basis set limit (CBS). Such high level potential energy surface calculations as a function of intrinsic reaction coordinate (IRC) reveal novel multidimensional tunneling dynamics and make possible preliminary estimates of the barrier height and tunneling splittings in the ground vibrational state.

The large-amplitude in-plane bending vibration of NCNCS at 85 cm⁻¹ has a potential energy function which includes a barrier to linearity with a height of about 285 cm⁻¹. The topology of the surface of the space defined by this two-dimensional potential function exhibits non-trivial monodromy. Therefore an energy/momentum map for a quantum system with its motion determined by such a potential takes the form of a lattice which contains a defect associated with the top of the barrier. In NCNCS, the wavenumber values of the fundamental vibrational excitation and the barrier height mean that easily accessible energy levels allow us to observe 3 bending vibrational levels below and 3 above the barrier, yet still below all of the other vibrational levels, allowing the study of all the levels in the neighborhood of the defect. In three measuring campaigns at the Canadian Light Source in May of the years 2011, 2012, and 2013 we have now obtained 8 of the 9 fundamental vibrational band systems of NCNCS in high resolution, in particular that of the large-amplitude bend in the FIR. So far only a-type spectra have been assigned. Thus we have now determined the ∆v_b = 1, and ∆K_a = 0 vibrational intervals (using bent molecule notation) but do not yet have experimental values for either rotational ∆K_a = +/− 1 intervals nor ro-vibrational ∆v_b = 1, ∆K_a = +/− 1 intervals. In May of 2014 we will have our last measuring campaign and hope to observe the more elusive b-type transitions.

We report on the analysis of our spectrum from 60-140 cm⁻¹ of the ν₇ bending fundamental and associated hot band sequence of NCNCS, obtained on the far-infrared beamline at the Canadian Light Source synchrotron. The data were collected in May 2013, building upon what we learned conducting experiments in May 2011 and 2012 on this molecule. Calculations indicated that the ν₇ system was very weak (one of the four weakest fundamental bands, all of comparable strength), but its spectrum became evident when 30 mTorr of NCNCS was admitted into the 2-m-long sample cell, through which the synchrotron beam passed 40 times. The best spectrum so far has been obtained with 121 mTorr of gas. Loomis-Wood plots reveal many branches, some of which were unambiguously assignable to ∆ν₇ = +1 subbands for ν₇^′′ = 0, 1, 2, 3 and for K_a = 0, 1,2 with ∆K_a = 0 (a-type subbands) by comparison of lower-state combination differences with those obtained from the published pure-rotational data. We will continue the analysis by assigning as many a-type subbands as possible and by searching for b-type subbands with ∆K_a = ±1 so that the connections between K_a-stacks can be measured. Finally, we will simultaneously fit the infrared and rotational data with a generalized semi-rigid bender Hamiltonian.

NCNCS is a quasi-linear molecule that displays plentiful spectroscopic signatures of transition from the asymmetric top to the linear rotor regime. The transition takes place on successive excitation of the ν₇ bending mode at ca 80 cm⁻¹. The unusual spectroscopic manifestations on crossing the barrier to linearity are explained by quantum monodromy and described quantitatively by the generalised semi-rigid bender Hamiltonian.^1,2,3 Nevertheless, analysis to experimental accuracy of the extensive mm-wave spectrum of NCNCS recorded with the FASSST technique has only so far been achieved with the use of separate J(J+1) expansions for each (v₇, K_a) transition sequence.^c In addition, several selective perturbations identified between transition sequences in different vibrational levels^c are still unfitted. Presently we seek effective approximations to the vibration-rotation Hamiltonian that would allow combining multiple sequences into a fit, would allow a perturbation analysis, and could use mm-wave data together with high-resolution infrared measurements of NCNCS made at the Canadian Light Source. The understanding of effective fits to low-K_a subsets of rotational transitions in the FASSST spectrum has already allowed confident assignment of the ³⁴S and both ¹³C isotopic species of NCNCS in natural abundance, as will be described.
-----
¹B.P.Winnewisser, et al., Phys. Rev. Lett. 95. 243002 (2005). ²M.Winnewisser, et al., J. Mol. Struct. 798, 1 (2006). ³B.P.Winnewisser, et al., Phys. Chem. Chem. Phys. 12, 8158 (2010).

The complexation of chlorofluorocarbons (CFCs) with atmospheric water and pollutants of the atmosphere affects their reactivity and it seems to accelerate, for example, the decomposition rate of freons in the atmosphere [1]. For this reason we characterized shapes, stabilities, nature of the non-covalent interactions, structures and internal dynamics of a number of complexes of CFCs with water and of their dimers or oligomers by rotational spectroscopy. It has been found that hydrogenated CFCs form adducts with other molecules through weak hydrogen bonds (WHBs). Their C-H groups can act as proton donors, enhanced by the electron withdrawing of the halogen atoms, interacting with the electron rich regions of the partner molecules [2]. Also in adducts or oligomers of hydrogenated CFCs the monomer units are held together by nets of WHBs [3]. When CFCs are perhalogenated, the positive electrostatic region (“σ-hole”) can interact electrostatically with negative sites of another, or of the same molecular entity, giving rise, according to IUPAC, to the so called halogen bond (HaB). However, it has been observed that when the perhalogenated CFCs has a Π electron system, a lone pair•••Π interaction (Bürgi-Dunitz) is favoured [4]. We describe here the HaBs that CF₄ and CF₃Cl form with a variety of partner molecules such as water, ammonia, dimethyl ether, etc. Important spectroscopic features outline strong dynamics effects taking place in this kind of complex. References [1] V. Vaida, H. G. Kjaergaard, K. J. Feierabend, Int. Rev. Phys. Chem. 22 (2003) 203. [2] See, for example: W. Caminati, S. Melandri, A. Maris, P. Ottaviani, Angew. Chem. Int. Ed. 45 (2006) 2438. [3] G. Feng, L. Evangelisti, I. Cacelli, L. Carbonaro, G. Prampolini, W. Caminati, Chem. Commun. 50 (2014) 171. [4] Q. Gou, G. Feng, L. Evangelisti, W. Caminati, Angew. Chem. Int. Ed. 52 (2013) 52 11888.