G. Wilse Robinson

Environmental perturbations on foreign atoms and molecules in solid argon, krypton and xenon

Perturbations which are responsible for the shifts of electronic and vibrational spectra of species trapped in a solid are considered in terms of the intermolecular potential which describes interactions between these species and neighbouring atoms. It is shown that in certain instances Londons theory can give an adequate approximation to the dispersion energy between an electronically excited species and a rare gas atom. The experimental shifts in the electronic absorption spectra of Hg, NH and C2 at lattice sites in rare gas crystals at 4·2°k are explained quantitatively on the basis of a Lennard-Jones (6-12) or (6-8-12) potential between the trapped species and the rare gas atoms. The theory does not adequately explain the shifts in those cases where strong angular dependent forces differing appreciably in the two electronic states are present, data on trapped NH2 free radicals being presented as a case in point. The interaction of sodium atoms with argon at 4·2°k is very complex, the data being consi...

Trapped NH2 Radicals at 4.2°K

A study has been made of the electronic absorption spectrum of the NH2 radical trapped in an argon matrix on a liquid helium cooled surface. The radical is produced in a microwave discharge of argon mixed with a small amount of parent molecule, ammonia or hydrazine. The long effective absorbing path is illustrated by the presence of new bands of NH2, too weak to have yet been observed in the flash photolysis spectrum. That the radicals have also been found in moderate concentration from low‐pressure discharges containing hydrogen and nitrogen in many forms indicates that they are easily built up from smaller fragments, a fact which may be important in the explanation of the origin of these radicals in comets. The radical is positively identified by the excellent correlation between the low temperature spectrum and the gas‐phase spectrum recently analyzed by Ramsay, and in agreement with this analysis only alternate bands appear strongly at 4.2°K. The observed features, which represent rotational lines of ...