THE VIBRATIONAL-SPECTRA OF MOLECULAR-IONS ISOLATED IN SOLID NEON .14.CH3F+, CH3CL+, CH(3)BR(+), AND THEIR YLIDION ISOMERS

When a Ne:CH(3)X (X=F, Cl, Br) sample is codeposited at approximately 5 K with neon atoms that have been excited in a microwave discharge, t he infrared spectrum of the resulting solid deposit includes prominent absorptions which can be assigned to cation products. It has previous ly been established that the ylidion (H(2)CXH(+)) isomers have stable potential minima and that H2CFH+ is lower in energy than CH3F+. The id entification of the new absorptions is aided by experimental studies o n isotopically substituted Ne:CH(3)X samples and by ab initio calculat ions of the structures and vibrational fundamentals of both CH(3)X(+) and H(2)CXH(+). In each of the three systems, a prominent absorption w hich is intermediate in frequency between the gas-phase (and neon-matr ix) absorptions of HX and HX(+) can be assigned to the ylidion, as can be several other absorptions. Still other absorptions can be assigned to CH3Cl+ and CH3Br+. The behavior of the product absorptions on expo sure of the deposit to filtered visible and ultraviolet radiation is c onsistent with the proposed assignments.