Mass Ratio of the Boron Isotopes from the Spectrum of BO

Wave number data. New measurements are made of the rotational structure of the α bands of BO, and the wave numbers of the lines in the ²Π1/2, ²Σ component up to about $J=20$ are tabulated for the (0, 0), (0, 1), (0, 2), (1, 0), (1, 1), (1, 2), (2, 0), (3, 0), and (4, 0) bands of both the B¹¹O and B¹⁰O systems. The ²Π1/2, ²Σ component of (5, 0) is also measured for B¹¹O and the ²Π3/2, ²Σ component of (1, 0) for B¹¹O and B¹⁰O.Vibrational isotope effect. Values of ΔGᵥ are computed by least-squares methods, and from the ratio ΔGₑⁱΔGₑ, the isotopic mass coefficient ρ=(μμⁱ)1/2 is found to be 1.02908±{}0.00003, from the data on the ²Σ state, and 1.02913±{}0.00004, from that on ²Π1/2. The latter figure is less trustworthy than the former, because of the presence of perturbations in the upper state. The mass-spectrograph measurements of Aston give ρ=1.02908±0.00003. The relation ρ=xₑⁱxₑ is verified to within the probable error, one part in 500. Improved values are obtained for the vibrational constants of the ²Σ state, while for the ²Π1/2 state, the equations ΔGᵥ=1260.415-21.870(v^'+1/2) and ΔGᵥⁱ=1297.130-23.228(v^'+1/2) are considered to give the constants least influenced by perturbation effects.Rotational isotope effect. From the rotational term-differences, the constants Bᵥ and α are computed, also by least squares. The equations Bᵥ^''=1.7803-0.01648(v^''+1/2), Bᵥ^''i=1.8850-0.01772(v,^''+1/2), Bᵥ^'i_-1/2=1.4277-0.0196(v^'+1/2), and B_v,-1/2^'i=1.5115-0.0211(v^'+1/2) give values of ρ²=BₑⁱBₑ and ρ³=αₑⁱαₑ which yield values of ρ equal to those obtained from the vibrational constants to within the probable error, one part in 4000 for the Bₑ's and one in 100 for the αₑ's. A perturbation is found in the rotational levels of ²Π1/2⁽⁴⁾, which reaches its maximum at J^'=131/2. It is caused by the crossing of these levels by those of ²Σ⁽¹⁷⁾, and affects only one component of the Λ-doublets, as expected. The Λ-doubling is investigated, and its constants computed.Electronic isotope effect The spin coupling constant, A, is evaluated by the 1, 0 band, and found to be the same for B¹¹O and B¹⁰O, having the value 122.36±{}0.03 cm^-1. The origins of the two isotopic band systems, ²Π1/2, ²Σ, are found to be ν₂ₑ=23,958.85±0.05, ν₂ₑⁱ=23,959.18±0.06, giving an electronic shift of 0.33±{}0.08 cm^-1, the B¹⁰O origin being displaced toward the violet.