High level ab initio calculations have been undertaken of potential energy curves of CO 2+ (and for the CO neutral ground state). The accuracy of the potentials was tested by a synthesis of the available vibrationally resolved threshold photoelectrons in coincidence (TPEsCO) and time of flight, photo electron photo electron coincidence (TOF-PEPECO) spectra of CO 2+ . Good agreement was found between experimental and theoretical spectra once relative energies of the calculated double ionization energies were slightly adjusted (by approximately 1%) to match experiment. Vibrational separations within individual electronic states are very well reproduced (the worst error is 0.07%).

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Midinfrared spectra of the formyl cation, HCO(+), were recorded by direct absorption in a glow discharge (composition CO, 50 mTorr; H2, 50 mTorr; He, 7 Torr) using a color center laser spectrometer and velocity modulation with heterodyne detection. The bands measured were 10(0)0-00(0)0, 11(1)0-01(1)0, 12(0)0-02(0)0, 12(2)0-02(2)0, 10(0)1-00(0)1, 11(1)1-01(1)1, 20(0)0-10(0)0, and 10(0)2-00(0)2. These bands were analyzed and fitted together with all other available rotationally resolved spectra to arrive at a new set of spectroscopic constants for HCO(+). The relative intensities were fit to obtain a rotational temperature, Trot = 434 ± 7 K, and vibrational temperatures for each mode, T1 = 3300 ± 240 K, T2 = 841 ± 15 K, and T3 = 3157 ± 68 K.

In our previous paper on HCO + , several molecular constants were incorrectly coded for the SPFIT 1 program. The effect of this error is that the original effective Hamiltonian is a transformation of the corrected effective Hamiltonian. As a result, the encoding errors had no effect on calculated line frequencies, and the original spectroscopic constants are related to the corrected spectroscopic constants by a linear transformation.Specifically, the l-dependent contribution to the energy from B υ and D υ was omitted for the 01 1 0, 01 1 1, 11 1 0, and 11 1 1 vibrational states. Furthermore, a portion of the contribution from g 1 to the 11 1 0 and 11 1 1 vibrational states was also omitted. As a result, the original values of B υ for the affected vibrational states are too large by 2D υ and the original values for G υ are too small by B υ + D υ for the 01 1 0, 01 1 1 states and B υ + D υ − g 1 for the 11 1 0 and 11 1 1 states. The errors in G υ result in corrections to the spectroscopic constants in the expansion of G υ .The corrected values for the affected spectroscopic constants are provided in Table 1. Data files for the corrected fit are provided as Supporting Information.

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