Identification of cyc-B(3)H(3) with Three Bridging B–H–B Bonds in a Six-Membered Ring

[Image: see text] Irradiation of samples of diborane(6), B(2)H(6) and B(2)D(6), separately and together, dispersed in solid neon near 4 K with tunable far-ultraviolet light from a synchrotron yielded new infrared absorption lines that are assigned to several carriers. Besides H, B, BH, BH(2), BH(3), B(2), B(2)H(2), and B(2)H(4), previously identified, a further species is assigned on the basis of quantum-chemical calculations of vibrational wavenumbers and intensities to be cyc-B(3)H(3) (D(3h), singlet state) in several isotopic variants, which feature three bridging B–H–B bonds in a six-membered ring.