The ro-vibrational predissociation spectrum of He-H₃⁺ has been recorded via excitation of the ν₂ vibrational mode of the H₃⁺ sub-unit in a cold 22-pole ion trap. The spectrum for the bare H₃⁺ consists of only a few ro-vibrational lines each for the para and ortho nuclear spin configuration, respectively. Instead, the spectrum of the complex is very rich (several hundred lines) even at the low temperature (4 K) of the trap experiment. Part of this complexity is associated with the (almost) free internal rotation of H₃⁺. The experimental results are compared to theoretical predictions of ro-vibrational spectra on the basis of ab-initio calculations of the He-H₃⁺ potential energy surface. The energy levels result in transitions which agree in many cases with experimental results within a few wavenumbers. In particular the typical band structures of a P- and R-branch associated with an effective diatomic complex seen in the experimental and predicted spectrum help in assigning the rich spectrum. Moreover, an experimental energy term diagram is reconstructed from the observed transitions which can be compared to the rather accurate theoretical predictions. Despite of the floppiness of the complex rotational constants for the effective diatomic complex can be derived and match to the term diagram of a prolate, slightly asymmetric rotor. The influence of the Coriolis interaction resulting from the H₃⁺ internal rotation in a rotating He-H₃⁺ frame shall be discussed.

Some time ago we developed a five dimensional SO(5) superrotor model [1] which describes the energy term diagram of the lowest energy states of CH₅⁺ surprisingly well [2]. The basis for this model lies in the S₅ permutation symmetry of the five identical protons in this molecule. In this contribution we discuss possible sub-group structures, in particular the embedded S₄⊗S₂ ⊆ S₅ ⊂ SO(5), which potentially simplifies the current model and more importantly can be associated with the internal motions (vibration/rotation/internal-rotation) of the molecule. As a result the ad-hoc SO(5) model motivated by the simple super-rotor energies can be replaced by a model justified by the underlying physics. [1] H. Schmiedt, P. Jensen, S. Schlemmer, Rotation-vibration motion of extremely flexible molecules – the molecular superrotor, Chem. Phys. Lett. 672 (2017), p. 34-46 [2] O. Asvany, K. M. T. Yamada, S. Brünken, A. Potapov, S. Schlemmer, Experimental ground-state combination differences of CH₅⁺, Science, 347 (2015), pp. 1346-1349

Ammonia is an important “weed” molecule in interstellar medium, planetary and exoplanetary atmosphere studies. In last ten years, new experimental IR analysis have been reported in the extended region between 5000 cm⁻¹(or 2 μm) and 10,000 cm⁻¹(or 1 μm). But before 2020, there was not a reliable NH₃ line list for the 6000 cm⁻¹(or 1.63 μm) region. We combined the line position predicted on our Ames-Pre3 potential energy surface and the 296K intensity predicted in the UCL-C2018 line list [Coles et al JQSRT (2018) 219, 199-212], to analyze the Kitt Peak FTS spectra archived at JPL. More than 1300 transitions (J=0-10) have been assigned to following bands in the range of 5700 - 6200 cm⁻¹: ν₂+ν₃+ν₄ (0111), ν₁+ν₂+ν₄ (1101), 3ν₂+ν₃ (0310), ν₁+3ν₂ (1300), and a "hot" band 2ν₂+ν₃+ν₄ (0211) - ν₂ (0100). The combination difference for the determined experimental energy levels are about 1E-3 cm⁻¹, close to the resolution of lab measurements. The Ames-Pre3 based line positions are usually found to be accurate within ± 0.05-0.10 cm⁻¹. Assignments and derived rovibrational levels will be compared to those reported recently in Cacciani et al [JQSRT (2021) 258, 107334].

Quasi-linear molecules display a large amplitude bending mode allowing them to sample their linear configuration. This leads to a strong coupling between the overall rotation and the bending mode and to a singularity in their Hamiltonian. Quasi-linearity has been extensively studied in many species including the closed shell water molecule and the open shell amidogen (NH₂) and methylene (CH₂) radicals. For these three species, the barrier to linearity ranges from 12 000 cm⁻¹ for NH₂ to less than 2000 cm⁻¹ for CH₂.Jungen, Hallin, and Merer, Molec. Phys. 40 (1980) 25; Bunker, Jensen, Kraemer, and Beardsworth, J. Chem. Phys. 85 (1986) 3724; Partridge and Schwenke, J. Chem. Phys. 106 (1997) 4618heir rovibrational energy levels can be computed with almost spectroscopic accuracy using variational approaches or, if a higher accuracy is required, with reduced dimensionality models such as the effective Bending-Rotation approach,Coudert, Marin-Drumel, and Pirali, J. Mol. Spectrosc. 303 (2014) 36lready applied to treat the anomalous centrifugal distortion of the water molecule^b and of the amidogen radical.TD03, Martin-Drumel, Pirali, and Coudert, 72nd ISMS, Urbana-Champaign, June 19-23, 2017n this talk, the Bending-Rotation approach^b is extended, adding the spin-rotation and spin-spin fine couplings, so as to be used in the case of the methylene radical. The new approach is applied to the fitting of high-resolution data pertaining to this species. In addition to the ground state data previously analyzed,Brünken, Müller, Lewen, and Giesen, J. Chem. Phys. 123 (2005) 164315he data set includes FIR transitions belonging to the ν₂ band.Sears, Bunker, and McKellar, J. Chem. Phys. 77 (1982) 5363; McKellar, Yamada, and Hirota, J. Chem. Phys. 79 (1983) 1220; and Marshall and McKellar, J. Chem. Phys. 85 (1986) 371636 transitions were reproduced with a standard deviation of 1.3 using 42 spectroscopic parameters.Coudert, J. Chem.\ Phys. 153 (2020) 144115n the talk, the results of this analysis will be reported and the dependence on the bending angle retrieved for the spin-rotation and spin-spin fine couplings will be discussed. We will also try to see if the analysis results^f can be further improved.

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Footnotes:

Jungen, Hallin, and Merer, Molec. Phys. 40 (1980) 25; Bunker, Jensen, Kraemer, and Beardsworth, J. Chem. Phys. 85 (1986) 3724; Partridge and Schwenke, J. Chem. Phys. 106 (1997) 4618T Coudert, Marin-Drumel, and Pirali, J. Mol. Spectrosc. 303 (2014) 36a TD03, Martin-Drumel, Pirali, and Coudert, 72nd ISMS, Urbana-Champaign, June 19-23, 2017I Brünken, Müller, Lewen, and Giesen, J. Chem. Phys. 123 (2005) 164315t Sears, Bunker, and McKellar, J. Chem. Phys. 77 (1982) 5363; McKellar, Yamada, and Hirota, J. Chem. Phys. 79 (1983) 1220; and Marshall and McKellar, J. Chem. Phys. 85 (1986) 37163 Coudert, J. Chem.\ Phys. 153 (2020) 144115I

We report spectroscopic studies of the cyclopropyl radical and cation (c-C₃H₅). The cation especially is unstable towards ring-opening to allylic geometries, and the radical exhibits tunneling splitting due to inversion tunneling by the α-H atom that lies out of the C-C-C ring plane¹. These large amplitude motion phenomena complicate the photoionization (and other) spectra and the determination of properties that are of interest due to ring strain in this fundamental cyclic radical. Through a multiscale reduced-dimension ab initio description of the potential energy surfaces of both the radical and the cation, the rotational and ionization spectra of the radical are simulated using advanced perturbative and variational rovibrational treatments. The results are compared with experimental photoionization data from the literature and new measurements². [1] Dong et al.; J. Phys. Chem. A; 2006; 110; 3059-3070. [2] Dyke et al.; J. Chem. Soc., Faraday Trans. 2; 1985; 81; 1573-1586.

With recent advances in ultrashort laser technology, many studies using intense nonresonant laser fields have been conducted to control vibrational or rotational wave packets. In particular, control of large-amplitude low-frequency vibration is important because such vibration may cause a substantial change in molecular structure. For instance, torsional motion of biphenyl has deserved much attention since chirality and physical properties of the molecule depend on its torsional angle. In this study, we coherently excite torsional vibration of substituted biphenyl derivatives by the interaction with ultrashort laser fields and the resultant vibrational excitation is monitored by recording resonant two-photon ionization (R2PI) spectrum. We further adopt double-pulse excitation to control vibrational state distribution via wave-packet interference. Adiabatically cooled molecular sample of 2-fluorobiphenyl is irradiated by the fundamental output from a fs Ti:Sapphire laser. This pump pulse induces vibrational excitation through impulsive Raman process. With an appropriate delay after the pump-pulse irradiation, the S₁−S₀ excitation spectrum of the molecules is recorded via R2PI with the doubled output of a nanosecond dye laser ( ∼ 280 nm). A progression with almost constant spacings appears in the R2PI spectrum without the pump pulse. It has been assigned to that of the torsional mode from vibrational ground state, i.e., v = 0 (v being the quantum number of the torsional mode in the electronic ground state).H. S. Im and E. R. Bernstein, J. Chem. Phys. 88, 7337 (1988).hen the pump pulse is introduced, the intensity of each band is reduced and new bands appear. These bands are assigned to the progression from v = 1. These observations indicate that impulsive Raman excitation of torsional vibration is realized. We also conduct a double-pump pulse experiment, where a pair of pulses are implemented for excitation. In this experiment, we succeeded in controlling the state distribution of torsional vibration by adjusting the time delay between the two pump pulses.

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Footnotes:

H. S. Im and E. R. Bernstein, J. Chem. Phys. 88, 7337 (1988).W

In this contribution, an application of the ring puckering coordinates (originally devised by Cremer and Pople) to the construction of one dimensional and two dimensional (2D) cuts of the potential energy surfaces (PESs) and to the characterisation of pseudorotational and rotational motions of five-term ring systems is proposed. Firstly, an analysis of 2D-PESs is presented. Special care is devoted to the aspect of symmetry in such 2D-PESs, and analytical formulations of the computed 2D-PESs using suitable functional forms with a limited set of parameters are provided. Secondly, solutions of each of the time-independent nuclear Schrödinger equations associated with the pseudorotational motions of three five-term ring systems are illustrated and discussed. In order to take into account the interplay between pseudorotational and rotational motions, the nuclear hamiltonian matrices are formulated for the azimuthal quantum numbers J = 0 and J = 1. The nuclear hamiltonian matrices are constructed and diagonalized using a Python program developed by the authors.

We have developed a wave packet imaging-based, broad bandwidth, high-resolution spectroscopic method for weakly bound molecular dimers. In the present method, rotational and intermolecular vibrational wave packet motion is induced in the molecular dimer, via impulsive stimulated Raman scattering upon femtosecond, broad bandwidth pulse irradiation. The subsequent rotational/vibrational motion is observed as a molecular movie, utilizing time-resolved Coulomb explosion imaging. Rotational and vibrational Raman spectra are obtained as Fourier transform of the observed time-dependent image parameters. In our present setup,  80 MHz frequency resolution and 1 THz bandwidth are achieved simultaneously. We have measured high-resolution spectra of Ar₂, (N₂)₂, and (CH₄)₂, while all of them are difficult targets for microwave spectroscopy due to their no or small permanent dipole. All measured spectra in the region of rotational transitions ( 150 GHz) show well-resolved structures. In the case of (N₂)₂ and (CH₄)₂, in which monomer units can rotate almost freely in the dimer, rotational constants vary with internal rotational states. This suggests internal motions govern the effective structures of the dimers. In addition to the rotational structure, the spectrum of (N₂)₂ shows a  250 GHz oscillation, which can be attributed to the fundamental band of an intermolecular vibration. These results indicate that the present approach is a powerful approach to study large-amplitude intermolecular dynamics. Details of the experimental setup and spectral analyses will be presented.

1,2-Benzenediol, commonly known as catechol, was investigated, an ortho substituted aromatic volatile organic compound (VOC) with two hydroxyl groups which, due to tunneling between two symmetrically equivalent structures, can interchangeably act as donor and acceptor in a weak hydrogen bond W. Caminati, S. Di Bernardo, J. Mol. Struct., 240, 263-274 (1990). Catechol displays appreciable gas-phase reactivity and its monitoring in the atmosphere via rovibrational spectroscopy has a strong interest. We performed a rotationally resolved analysis of the “free” and “bonded” –OH torsion modes of the intramolecular H-bond using synchrotron-based FT-Far-IR spectroscopy at the AILES beamline of SOLEILJ.B. Brubach, L. Manceron, M. Rouzieres, O. Pirali, D. Balcon, F. K. Tchana, V. Boudon, M. Tudorie, T. Huet, A. Cuisset, P. Roy, AIP Conf. Proc. 1214, 81–84 (2009). High level of theory anharmonic quantum chemistry calculations were required for the rovibrational assignement. Numerous series of hot bands involving the lowest vibrational energy modes are observed and a set of anharmonic parameters is proposed. Finally, using a millimeter-wave spectrometer,G. Mouret, M. Guinet, A. Cuisset, L. Croizé, S. Eliet, R. Bocquet, F. Hindle, IEEE Sens. J. 13, 133-138 (2013).he room temperature Doppler limited rotational spectrum of catechol has been measured in the 70-220 GHz frequency range. Pure rotational lines belonging to the ground and the four lowest energy vibrationally excited states have been assigned. Splitting due to the tunneling were resolved for the free –OH torsion state and a global fit gathering the far-IR and millimeter-wave data provides the rotational parameters of the low-energy far-IR modes, especially those involving the intramolecular hydrogen bond. W. Caminati, S. Di Bernardo, J. Mol. Struct., 240, 263-274 (1990).. J.B. Brubach, L. Manceron, M. Rouzieres, O. Pirali, D. Balcon, F. K. Tchana, V. Boudon, M. Tudorie, T. Huet, A. Cuisset, P. Roy, AIP Conf. Proc. 1214, 81–84 (2009).. G. Mouret, M. Guinet, A. Cuisset, L. Croizé, S. Eliet, R. Bocquet, F. Hindle, IEEE Sens. J. 13, 133-138 (2013).t

One of the main objectives in the study of weakly bound complexes is to provide a quantitative description of the (ro)vibrational dynamics which can be dominated by nuclear quantum effects. For example, water and carbon monoxide form a weakly bound complex where the H₂O moiety can undergo a large-amplitude tunneling motion within the complex that exchanges the free and bound hydrogen atoms in the intermolecular bond. The exchange symmetry of identical particles entangles the spin and spatial quantum states of H₂O such that in the ground vibrational state, the symmetric tunneling state A correlates with para-H₂O (I=0), while the antisymmetric tunneling state B correlates with ortho-H₂O (I=1). The gas phase water-CO complex has been extensively studied by microwaveD. Yaron, K. I. Peterson, D. Zolandz, W. Klemperer, F. J. Lovas, R. D. Suenram, J. Chem. Phys. 92, 7095 (1990).R. E. Bumgarner, S. Suzuki, P. A. Stockman, P. G. Green, G. A. Blake, Chem. Phys. Lett. 176, 123 (1991). and IR spectroscopyM. D. Brookes, A. R. W. McKellar, J. Chem. Phys. 109, 5823 (1998).L. Oudejans, R. E. Miller, Chem. Phys. Lett. 306, 214 (1999).A. J. Barclay, A. van der Avoid, A. R. W. McKellar, N. Moazzen-Ahmadi, Phys. Chem. Chem. Phys. 21, 14911 (2019).nd when compared with full-dimensional quantum bound state calculations on a nine-dimensional potential energy surface, the agreement is very good.P. M. Felker, Z. Bacic, J. Chem. Phys. 153, 074107 (2020).e have completed analogous IR studies of the tunneling splittings of the water-CO complex when the complex is isolated in a parahydrogen quantum solid. We can estimate the tunneling splittings in the ground and excited (CO stretch, water stretch, and water bend) vibrational states to see how the tunneling motion is perturbed by the presence of the quantum solid. Furthermore, we can examine the nuclear spin conversion kinetics between the two tunneling levels in the ground vibrational state by rapidly changing the temperature of the sample. Nuclear spin conversion has not been reported in the previous gas phase studies and thus these are the first results for this water-CO complex. D. Yaron, K. I. Peterson, D. Zolandz, W. Klemperer, F. J. Lovas, R. D. Suenram, J. Chem. Phys. 92, 7095 (1990).

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Footnotes:

M. D. Brookes, A. R. W. McKellar, J. Chem. Phys. 109, 5823 (1998).

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Footnotes:

A. J. Barclay, A. van der Avoid, A. R. W. McKellar, N. Moazzen-Ahmadi, Phys. Chem. Chem. Phys. 21, 14911 (2019).a P. M. Felker, Z. Bacic, J. Chem. Phys. 153, 074107 (2020).W

At previous ISMS meetings we have reported on the effects of monodromy on the ν₇ bending mode of NCNCS. The presence of monodromy was established directly from experimental data collected at the Canadian Light Source. To aid that work we assigned some of the spectrum of the ν₇ manifold built on the ν₃ stretching mode. In this talk we will discuss a more complete assignment of the ν₃+ν₇ spectrum. One of our goals is to consider the impact of stretching on the monodromy of the ν₇ mode. We will attempt to use the same Generalized SemiRigid Bender model as was applied to the pure ν₇ mode.