A reanalysis of the interstellar CH abundance

An analysis of historic interstellar CH abundance and electronic state data for the interstellar medium was undertaken to identify the term structures of various electronic states and to identify errors in previous analyses. Attention was devoted to the X(2)Pi, A(2)Delta, B(2)Sigma(-), and C(2)Sigma(+) systems. Error sources were identified as neglect of the Lambda doubling of ground state. The splitting causes a doubling of the oscillator strength of lines from the B-X and C-X electronic systems, blending of two lines appearing as 4300, 3886, and 3143 A lines, the inaccurate identification of which half of the Lambda doublet generated the lines, and no accurate determination of the excitation temperature. Examples are furnished of CH Lambda ground state data from Delta Per, Delta Oph, X Per, and Chi Oph using equivalent widths to show an inverted Lambda doublet, that a radio maser can be detected optically, and a match between the X Per and Delta Per theoretical and measured temperatures.