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FLASH photolysis of arsine a t -20 mm. Hg pressure has yielded two new groups of sharp absorption bands which are attributed to the ASH and ASH, free-radicals. These assignments have been confirmed by the isotope shifts observed using fully deuterated arsine, AsD,.Arsine was prepared by the method described by Jolly,l and the deuteroarsine by the action of deuterium oxide on aluminium arsenide. The infrared spectra of the ASH, and AsD, showed negligible absorption from impurities. The electronic spectra were photographed in the first and second orders of a 21 f t . concave grating spectrograph with an absorption path of 1 metre. The half-lives of both species under the above conditions are -60psec.

Two new band systems have been observed in absorption following flash photolysis of AsH 3 and AsD 3 , and are assigned to 2 A 1 - 2 B 1 electronic transitions of AsH 2 and AsD 2 . The origins of both systems are at 19905 cm -1 . The bands have the complex rotational structure associated with an asymmetric rotor. Rotational analyses have been carried out for three bands of the AsH 2 spectrum, leading to the following molecular parameters: ground state, r" 0 = 1.518 Å valence angle = 90° 44'; excited state, r' 0 = 1.48 Å, valence angle = 123° 0'. The parameters associated with rotation about the a inertial axis increase rapidly with increase in v' 2 . The spectrum shows doublet splittings of up to 41 cm -1 , and the excited state furnishes the first example of a doublet state of an asymmetric top molecule which shows substantial departures from Hund’s case ( b ).

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