Simultaneous Measurement of HI Fundamental and Overtone Lines

Abstract

Measurements of absorption line intensities in the HI overtone band at 2.3 μ have been undertaken by a method of comparison with lines in the fundamental. The technique employed lends itself particularly well to the obtaining of consistent data from two bands, which is most important for the determination of the coefficients of the dipole-moment function. These considerations led to the selection of the six overtone lines P (2) through R (3) for measurement. One interesting aspect of the overtone intensities and matrix elements is the similarity of their magnitudes to those of the fundamental. Thus, extrapolating from the measured data to obtain a total overtone band intensity, a value of 0.19±0.02 cm—2 atm—1 at 300°K is deduced. This is more than half the fundamental-band intensity. On the other hand, as contrasted with the fundamental, there is virtually no distortion of the overtone band arising from the interaction of vibration and rotation. Consideration of all the data thus far collected on HI leads to the conclusion that the fundamental matrix elements must be negative and the overtone matrix elements positive. Likewise, it may be inferred that the value of θ2=M2re/M1 is about —5.