The Lifetime of Free Hydroxyl

Abstract

(1) The reasons for various failures to observe the absorption spectrum of free hydroxyl radicals are discussed. (2) The absorption spectrum of OH in the electric discharge through water vapor is observed with a spectrograph of high resolving power. After interrupting the discharge, the presence of OH is traced by its absorption spectrum over time intervals up to 1/8 sec. (3) With alternating half‐periods of 60 cycle a.c. cut out by a switch, the emission of OH vanishes almost entirely with the current whereas the absorption persists rather uniformly. It is concluded that the persistence of the absorption spectrum is to be attributed to a long life of OH radicals rather than a long life of O and H atoms furnishing a fresh supply of short life OH radicals. (4) The rotational intensity distribution within the OH band at strong currents (being anomalous to a lesser extent than at faint currents) indicates the presence of free OH in the discharge. (5) For a comparison of the present result with previous estimates, leading to a much shorter life of free hydroxyl, the number per sec. of emission processes of the OH band is measured, assuming that each of these processes leads to the production of one free OH radical. (6) The process by which OH radicals are consumed is discussed.