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Reexamination of the C2H3+ microwave and infrared spectra



Jon T. Hougen, Laurent H. Coudert


The high-resolution infrared spectrum of C2H3 recorded in the 3 CH stretching region (J. Phys. Chem. 99 (1995) 15611-15623) is re-analyzed using an effective internal axis method (IAM) accounting for the large amplitude hydrogen migration motion. The line position analysis carried out with this approach allows us to fit 63% of the data with a standard deviation of 0.1 cm-1, using 11 parameters, including the band center, the semi-rigid rotator spectroscopic constants, and three parameters corresponding to the magnitude of the tunneling splitting and to its rotational dependence. In agreement with the IAM approach, this rotational dependence is described by an angle theta, which can also be calculated theoretically by making several assumptions about the geometry of the ion along the tunneling path. The agreement between fitted and calculated values of theta gives partial confirmation of these geometrical assumptions and provides us with further insight into the nature of the hydrogen migration motion. In the present analysis, observed minus calculated residuals for 37% of the available high-resolution data are greater than 0.1 cm-1. This is believed to be due to random perturbations by dark states.
Journal of Molecular Spectroscopy


hydrogen migration, infrared spectrum, least squares fit, protonated acetylene ion, rotational levels, theoretical tunneling model


Hougen, J. and Coudert, L. (2011), Reexamination of the C2H3+ microwave and infrared spectra, Journal of Molecular Spectroscopy, [online], (Accessed June 22, 2024)


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Created September 29, 2011, Updated February 19, 2017