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The Napier (relaxation) frequency of oxygen has been determined as a function of methane and deuterated methane impurity at room temperature and at 100°C, using the pressurized Kundt's tube developed in this laboratory. Methane is three times as effective as hydrogen itself, and is comparable with water vapor in causing shift to higher frequencies. Deuterated methane is about 14 as effective. The shifts are in all cases linear with the (small) concentration, up to 2%.
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Urban E. Schnaus (1965) studied this question.
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