ESR investigations of H\u3csub\u3e2\u3c/sub\u3eO\u3csup\u3e+\u3c/sup\u3e, HDO\u3csup\u3e+\u3c/sup\u3e, D\u3csub\u3e2\u3c/sub\u3eO\u3csup\u3e+\u3c/sup\u3e, and H\u3csub\u3e2\u3c/sub\u3e\u3csup\u3e17\u3c/sup\u3eO\u3csup\u3e+\u3c/sup\u3e isolated in neon matrices at 4 K.

The H2-‰ 1 6O+, HD-‰1 6O+, D2-‰ 1 6O+, and H2-‰ 1 7O+ ion radicals have been generated by photoionization, trapped in neon matrices at 4 K, and investigated by ESR(electron spin resonance)spectroscopy. The magnetic parameters are g iso=2.0093(3), A iso(H)=73.7(6) MHz, and A iso(1 7O)=83.5(6) MHz. A weak electronic absorption feature at 6036(3) Ã… was observed which is tentatively assigned to a known gas phase band. The H2O+ radical appears to be rotating in neon and exhibits an unusual intensity increase as the matrix temperature is lowered from 9 to 4 K. Comparisons between H2O+ and the isoelectronic radicals NH2, NH+ 3, and CH3 are made