High-resolution oscillator strength measurements of the v′ = 0,1 bands of the B-X, C-X, and E-X systems in five isotopologues of carbon monoxide

We report oscillator strengths for six strong vibrational bands between 105.0 and 115.2 nm, associated with transitions from the v = 0 level of the X ¹Σ⁺ ground state to the v = 0 and 1 levels of the B ¹Σ⁺, C ¹Σ⁺, and E ¹Π states, in ¹²C¹⁶O, ¹²C ¹⁷O, ¹²C¹⁸O, ¹³C¹⁶O, and ¹³C¹⁸O. These measurements extend the development of a comprehensive database of line positions, oscillator strengths, and linewidths of photodissociating transitions for all astrophysically relevant CO isotopologues. The E-X bands, in particular, play central roles in CO photodissociation and fractionation models of interstellar clouds and circumstellar disks including the early solar nebula. The resolving powers of the room-temperature measurements, R = 300,000-400,000, allow for the analysis of individual line strengths within bands; the measurements reveal J-dependences in the branch intensities of the C(v = 0,1)-X(0) and E(v = 0,1)-X(0) bands in all isotopologues. Minimal or no isotopologue dependence was found in the f-values of the C(v = 0,1)-X(0) and E(v = 0,1)-X(0) bands at a ∼5% uncertainty level. Revised dissociation branching ratios for the C(v = 0,1) and E(v = 0,1) levels are computed based on these f-values. The weak isotopologue dependence of the f-values presented here eliminates this mechanism as an explanation for the large ¹⁷O enrichments seen in recent laboratory photolysis experiments on CO at wavelengths from 105 to 108 nm.