Direct potential fit analysis of the X 1Σ+ ground state of CO

Abstract

A collection of 21,559 highly precise spectroscopic line positions from pure rotational and vibration-rotational spectra for seven isotopomers of carbon monoxide in the X1sigma+ ground electronic state has been employed in direct least-squares fits of the rovibrational Hamiltonian operator obtained from Watson's work [J. Mol. Spectrosc. 80, 411 (1980)] and that obtained by Herman and Ogilvie [Adv. Chem. Phys 103, 187 (1998)]. Fully analytical models are used for the various functions, including the Born-Oppenheimer internuclear potential function, and an account is taken of breakdown of the Born-Oppenheimer approximation. The resulting representations are more compact than currently available traditional Ukl/deltakl extended Dunham descriptions, and they generate quantum-mechanical eigenvalues that reproduce reliably the spectroscopic line positions to within the associated measurement uncertainties. Rayleigh-Schrodinger perturbation theory has been used to calculate highly accurate rotational and centrifugal distortion constants Bupsilon-Oupsilon for nine isotopomers of carbon monoxide. These constants are just as successful at reconstructing the observed spectroscopic information as the quantum-mechanical eigenvalues of the fitted Hamiltonian operators.

UV-frequency metrology on CO (a3Π): Isotope effects and sensitivity to a variation of the proton-to-electron mass ratio

“…This suggests that the ground state is probably the source of the discrepancy. Calculations using the LEVEL program [34] were performed to estimate the effects of the breakdown of the Born-Oppenheimer approximation in the ground-state of CO following the approach by Coxon and Hajigeorgiou [31]. The calculated energy difference between the 12 C 18 O and 13 C 16 O isotopologues was approximately 50 times smaller than observed in our measurements and is thus insufficient to explain the observed effect [35].…”

“…The shift was calculated with respect to 12 C 16 O. For the X 1 Σ + state the vibrational constants were obtained from fitting to the data from Coxon et al [31], while for the a 3 Π state the constants from Havenith et al [7] were used. In the lower panel, the difference between the experimental and calculated values of the band origins for the different isotopologues are plotted.…”

VIS and VUV spectroscopy of 12C17O and deperturbation analysis of the A1Π, υ = 1–5 levels

“…Rovibronic term values of the B O ground state, were calculated by using the B ) X (0, 0) and C ) X (0, 0) transition frequencies obtained from a VUV-FTS experiment and using the ground state molecular parameters by Coxon et al, 80 given for the 12 C 17 O The estimated absolute calibration 1s uncertainty was 0.005 cm À1 . Lines marked with 'w' were weak, and with 'b' were blended in the spectra.…”

Perturbations in the A1Π,v= 0 state of12C18O investigated via complementary spectroscopic techniques

“…22]. A comprehensive analysis was made by Coxon and Hajigeorgiou [23] leading to a very accurate model for the ground-state in CO isotopologues expressed in terms of molecular parameters.…”