Vibrational satellites in the microwave spectrum of cyclopropylidene methanone: Extension of rigid and semirigid bender calculations to larger molecules |
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| Institution: | 1. Technische Universität Berlin, Institut für Chemie, Theoretische Chemie, Sekr. C 7 Strasse des 17. Juni, 135 D-10623 Berlin, Germany;2. Institute of Chemistry and The Lise Meitner-Minerva Center for Computational Quantum Chemistry, The Hebrew University, Jerusalem 91904, Israel;1. Department of Experimental Psychology, University of Oxford, United Kingdom;2. Research School of Psychology, Australian National University, Australia;1. State Key Laboratory of Urban Water Resource and Environment, School of Environmental, Harbin Institute of Technology, Harbin 150090, China;2. College of Environment, Zhejiang University of Technology, Hangzhou 310032, China;3. School of Environmental and Biological Engineering, Nanjing University of Science and Technology, Nanjing 210094, China;1. Istituto Nazionale di Ricerca Metrologica, Strada delle Cacce 91, 10135 Torino, Italy;2. Department of Applied Science and Technology, Politecnico di Torino, Corso Duca Degli Abruzzi 24, 10129 Torino, Italy;3. Department of Agricultural, Forestry, and Food Sciences (DISAFA), University of Turin, Largo Paolo Braccini 2, 10095 Grugliasco, TO, Italy;4. Centro di ricerca per l''enologia (CREA-ENO), Via Pietro Micca 35, 14100 Asti, Italy;5. Department of Chemistry and NIS Inter-Departmental Centre, University of Torino, Torino 10125, Italy |
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| Abstract: | The microwave spectrum of cyclopropylidene methanone (CPM) at room temperature includes a large number of vibrational satellites. It has been possible to assign the spectrum of the ground state and nine additional series of satellites. Assignment to vibrational states with up to four quanta of the low-lying out-of-plane (ν15) and two quanta of the in-plane (ν21) bending modes was made by use of several lines of argument: - 1.(i) relative intensities of lines of the same vibrational state for determination of the parity;
- 2.(ii) variation of A and B-C with vibrational quantum number in comparison with model calculations for in-plane and out-of-plane bending of the heavy atoms;
- 3.(iii) identification of members of the same vibrational sequence by inspection of quotients of differences of their rotational constants.
We have generalized the bender method of Bunker et al. for numerical application to larger molecules. Resulting formulae are given in the text. The rigid bender model was used to fit the changes in rotational constants of the vibrational satellites of the out-of-plane bending mode to a double minimum potential with a barrier of 38.1 ± 0.8 cm−1 and minima at ±17.0 ± 0.1°. The ground state lies 5 cm−1 below the barrier. The in-plane bend is almost harmonic. Its frequency of 197 cm−1 was determined from an analysis of a Coriolis interaction of the v15 = 3, v21 = 0 state with the v15 = 0, v21 = 1 state. The vibrational-state dependence of the centrifugal distortion constants could be at least qualitatively reproduced in this model. The vibrational satellite shifts are equally well fitted when semirigidity is included as suggested by ab initio 4–31G MO calculations. In this case the barrier is slightly lower and the frequencies of ν15 and ν21 decrease by ca. 20%. On the basis of the experimental data presented here it cannot be decided whether the inclusion of semirigidity is necessary.Because the ground state out-of-plane vibrational wavefunction is practically constant over a wide range of the bending coordinate we term CPM quasisymmetric. |
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