Open AccessDoppler effects and intensities of lines in the molecular spectrum of hydrogen positive rays
Author(s) -
M. C. Johnson
Publication year - 1927
Publication title -
proceedings of the royal society of london. series a, containing papers of a mathematical and physical character
Language(s) - English
Resource type - Journals
eISSN - 2053-9150
pISSN - 0950-1207
DOI - 10.1098/rspa.1927.0070
Subject(s) - balmer series , excited state , atomic physics , ionization , spectral line , doppler effect , physics , ion , chemistry , line (geometry) , emission spectrum , quantum mechanics , geometry , mathematics
It is known from the work of Fulcher, Merton, Richardson, and others, that definite groups of lines in the secondary spectrum of hydrogen are strengthened in certain types of discharge. The interpretation of these phenomena in terms of specific molecular excitations has been begun by Richardson, on the basis of his classification of associated groups into bands. In the present paper the grouping of lines in the secondary spectrum is studied by longitudinal observation of positive rays in hydrogen. The optical spectrum of positive rays may be used in the following ways to contribute to the elucidation of the mechanisms of this spectrum. Firstly, the grouping of lines when excited by the impact of positive ions falling through a potential of several thousand volts can be examined. This can be compared with the grouping due to the impact of electrons at low voltages comparable with the ionisation potentials, and with the grouping in the Geissler tube spectrum. Secondly, a large Doppler effect appears in the Balmer lines when the positive rays are photographed longitudinally. From this can be determined what proportion of the atomic spectrum is carried by neutralised positive rays, and what proportion is excited in the stationary gas by the impact of positive ions. Further, it is possible to decide in some cases which of the Balmer line carriers have been free atoms in the positive rays stream, and which are recently dissociated molecular positive rays. These proportions are found to vary along the Balmer series. They can thus be related to the intensity grouping of the adjacent regions of the molecular spectrum. Thirdly, previous investigators of the secondary hydrogen spectrum in positive rays have, with one exception, agreed there is no Doppler effect in that spectrum. The exception is Rau, who by an ingenious indirect method showed eight extremely faint components. In the present work some further Doppler components have been found, and the intensity indicated below which any other components must lie. Evidence is thus obtained as to which of the lines in the secondary spectrum are mainly due to the excitation of stationary molecules, and which are carried by neutralised positive rays. This can be compared with the phenomena of the Richardson electron discharges, for which other evidence is available as to the mode of excitation.