Complete experimental rovibrational eigenenergies of HCN up to 6880 cm(-1) above the ground state

The [H, C, N] molecular system is a very important model system to many fields of chemical physics and the experimental characterization of highly excited vibrational states of this molecular system is of special interest. This paper reports the experimental characterization of all 3822 eigenenergies up to 6880 cm(-1) relative to the ground state in the HCN part of the potential surface using high temperature hot gas emission spectroscopy. The spectroscopic constants for the first 71 vibrational states including highly excited bending vibrations up to nu(2) = 10 are reported. The perturbed eigenenergies for all 20 rotational perturbations in the reported eigenenergy range have been determined. The 11 070 eigenenergies up to J = 90 for the first 123 vibrational substates are included as supplement to this paper. We show that a complete ab initio rovibrational analysis for a polyatomic molecule is possible. Using such an analysis we can understand the molecular physics behind the Schrodinger equation for problems for which perturbation theoretical calculations are no more valid. We show that the vibrational structure of the linear HCN molecule persists approximately up to the isomerization barrier and only above the barrier the accommodation of the vibrational states to the double well structure of the potential takes place

Saddle point localization of molecular wavefunctions

The quantum mechanical description of isomerization is based on bound eigenstates of the molecular potential energy surface. For the near-minimum regions there is a textbook-based relationship between the potential and eigenenergies. Here we show how the saddle point region that connects the two minima is encoded in the energy levels and wave functions of the potential energy surface

Spectroscopic characterization of isomerization transition states

Transition state theory is central to our understanding of chemical reaction dynamics. We demonstrate a method for extracting transition state energies and properties from a characteristic pattern found in frequency-domain spectra of isomerizing systems. This pattern—a dip in the spacings of certain barrier-proximal vibrational levels—can be understood using the concept of effective frequency, ω[superscript]eff. The method is applied to the cis-trans conformational change in the S[subscript 1] state of C[subscript 2]H[Subscript 2] and the bond-breaking HCN-HNC isomerization. In both cases, the barrier heights derived from spectroscopic data agree extremely well with previous ab initio calculations. We also show that it is possible to distinguish between vibrational modes that are actively involved in the isomerization process and those that are passive bystanders.National Science Foundation (U.S.) (NSF Graduate Research Fellowship DGE 1144083)Alexander von Humboldt-Stiftung (Feodor Lynen fellowship)United States. Department of Energy (Grant DE-FG0287ER136

Line Position and Line Intensity Modelings of H218O up to the First Triad and J = 20

International audienceLine position and line intensity analyses are carried out for the H218O isotopic species of the water molecule. Both datasets involve the five lowest lying vibrational states. For the line position analysis, the dataset includes infrared and far infrared transitions recorded in this work using high-temperature Fourier transform emission spectroscopy. Also included are already published infrared, far infrared, microwave, terahertz, Doppler-free combination differences, and kHz accuracy lines. The fitting is carried out with the bending–rotation approach and allows us to reproduce 12 858 line positions involving levels with J ≤ 20 and Ka ≤ 18, with a unitless standard deviation of 1.9, varying 207 spectroscopic parameters. For the line intensity analysis, far infrared line intensities measured in this work using Fourier transform spectroscopy in addition to previously measured line intensities are fitted. 5612 line intensities are accounted for with a unitless standard deviation of 1.5. The results from both analyses are used to build a line list for atmospherical purposes, spanning the 2–5000 cm−1 spectral range and containing 7593 lines. This line list and calculated energies and line intensities are compared to those already published

High-resolution infrared study of vinyl acetylene: The nu(13) (214 cm(-1)) and nu(18 ) (304 cm(-1)) fundamentals

The high resolution vibrational spectrum of vinyl acetylene (C2H3CCH) has been investigated in the far infrared region from 180 to 360 cm(-1) using the Bruker IFS 120 HR spectrometer at Justus-Liebig-Universitat, GieEen, Germany. The two energetically lowest vibrational fundamentals nu(13) and nu(18) at 214 cm(-1) and 304 cm(-1), respectively, were measured at a resolution of 0.0016 cm(-1). In addition to the fundamental modes, several hot bands originating from either nu(13) or nu(18) were observed and analyzed. The spectroscopic analysis was supported by high-level quantum-chemical coupled-cluster calculations and also made use of the Automated Spectral Line Assignment Procedure, ASAP, outlined earlier (MartinDrumel et al., 2015). In addition to the infrared study, so far unpublished millimeter-wave vibrational satellites that were measured in the course of an earlier study of the pure rotational spectrum of vinyl acetylene in its ground vibrational state (Thorwirth and Lichau, 2003) were added to the data set and are reported here for the first time. (C) 2021 Elsevier Inc. All rights reserved