Comments on "Global multi-isotopologue fit of measured rotation and vibration-rotation line positions of CO in X1σ+ state and new set of mass-independent Dunham coefficients"

In a recent paper [Velichko TI, Mikhailenko SN, Tashkun SA, Global multi-isotopologue fit of measured rotation and vibration-rotation linepositions of COin X1 S state and new set of mass-independent Dunham coefficients. J Quant Spectrosc Radiat 2012;113:1643-55], mass-independent Dunham coefficients were determined in a global fit of all available pure rotational and vibrational-rotational spectroscopic data for seven iso- topologues of the ground X1 S electronic state of carbon monoxide. Comparisons were made with previous sets of molecular constants, including the quantum-mechanical constant sobtained in 2004 [Coxon JA, Hajigeorgiou PG. Direct potential fit analysis of the X1 S ground state of CO. J Chem Phys 2004; 121: 2992-3008]. Velichko et al. reported apparent large errors in spectroscopic line positions calculated from the set of constants of Coxon and Hajigeorgiou. It is shown here that the calculations of Velichko et al. are in correct and that the molecular constants reported by Coxon and Hajigeorgiouare accurate and reproduce all relevant spectroscopic line positions to the same degree of precision as that achieved in the direct potential fit analysis.