2015ApJ...809..122B

We use the Sternberg et al. theory for interstellar atomic to molecular hydrogen (H i-to-H₂) conversion to analyze H i-to-H₂ transitions in five (low-mass) star-forming and dark regions in the Perseus molecular cloud, B1, B1E, B5, IC348, and NGC1333. The observed H i mass surface densities of 6.3-9.2 are consistent with H i-to-H₂transitions dominated by H i-dust shielding in predominantly atomic envelopes. For each source, we constrain the dimensionless parameter, and the ratio, of the FUV intensity to hydrogen gas density. We find values from 5.0 to 26.1, implying characteristic atomic hydrogen densities 11.8-1.8/cm3, for appropriate for Perseus. Our analysis implies that the dusty H i shielding layers are probably multiphased, with thermally unstable UNM gas in addition to cold CNM within the 21 cm kinematic radius.