Wave Lengths of the CH Band Lines

Evidence has recently been put forward by the writer 1 which indicated that several sharp, previously unidentified, interstellar lines were possibly due to transitions from the ground states of certain diatomic compounds, particularly the molecules CH, CN, and NaH.It was pointed out that if the proposed identifications were true, certain other lines, somewhat less intense than those already found, should be present and that the detection of these fainter lines would constitute a satisfactory proof that the sharp interstellar lines actually were caused by absorption by the abovementioned diatomic molecules.At the writer's suggestion, Dr.Adams kindly secured, with the coudé spectrograph of the Mount Wilson Observatory, some excellent spectrograms of the star Zeta Ophiuchi, in the spectrum of which the interstellar line at À4300.3, attributed to CH, occurs with greater strength than in any stellar spectrum yet investigated.On these spectrograms Adams found, 2 unmistakably, the three predicted CH lines near \ 3880 and not only their wave lengths but their relative intensities were very closely as predicted.Thus, since the evidence indicating that the CH molecule is responsible for the production of these lines is now so conclusive, it is important to secure with the greatest possible accuracy the laboratory wave lengths of the CH band lines, particularly of those mentioned above.This paper deals with a discussion of all the available wave-length data on the CH bands for the purpose of deciding upon the best laboratory values.0,0 2 A, 2 n band at À4315 Laboratory wave lengths of the some three hundred lines composing this band, known to astrophysicists also as the Fraunhofer G band, were measured by Heurlinger and Hulthén in 1918. 3Their values have been used during the last two decades