The R0(0) line of the 3s2A′1←2p2A″2 transition of the H3 radical has been observed in absorption by the new technique of photo-assisted fragmentation spectroscopy. A fast beam of metastable H3 radicals produced by H3 +/K electron transfer is interacted with visible light from a dye laser. Optical absorption is detected by observing a decrease in parent peak intensity in the H3 + neutralization-reionization mass spectrum, resulting from dissociation of the neutral molecule. Absorption line widths are observed to be instrumentally limited (≈ 0.05 cm-1) as the upper state of the transition is spectroscopically long lived. Application of the technique to various second-row hypervalent hydride radicals is discussed.