Microwave spectrum of the HCO radical

Abstract

The microwave spectrum of the K ‐doublet transitions of the free radical HCO has been observed in the N = 1, 2, and 3 rotational levels. The spectrum was analyzed and the following spectroscopic parameters were determined from the data: B − C = 2836.38 ± 0.45 MHz, ε = 224.62 ± 0.65 MHz, |ε_{z z}| = 8.12 ± 0.48 GHz, τ = 5.06 ± 0.13 MHz, D = 0.049 ± 0.019 MHz. The newly measured rotational constant was used along with previously measured constants to determine that the geometry of the HCO radical is r_CH = 1.11 Å, r_CO = 1.17 Å, θ_HCO = 127°.