Non-LTE models showing radiative excitation of the 5.29 GHz CH₂NH line. Top row: line radiation temperature, bottom row: optical depth. The horizontal axis in all plots is the H₂ density. The horizontal black dotted line indicates a vertical axis value of 0.0 on each plot. The violet horizontal dotted line indicates the observed brightness temperature toward IC 860. The horizontal thick red dashed line indicates the optical depth limit indicated by van der Tak et al. (2007) as line brightness temperatures may not be trusted if the optical depth is less than −0.1. Column densities for each pair of φ are labeled at the top of each pair of columns. Temperatures of the molecular gas are labeled in the upper left corner. The line width input to the mean escape probability approximation is 100 km s⁻¹. The maser action of CH₂NH in an infrared radiation field is observed in all cases from 10² cm⁻² to ∼10⁵ cm⁻².