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The contributions from arbitrary genus surfaces to the string propagator are investigated. Operator methods are applied using complete sets of string fields proposed by Krichever and Novikov. Metric variations related to boundary reparametrisations are treated on an equal footing with those related to deformations of the conformal structure. This results in an integral over additional moduli corresponding to averaging over boundary reparametrisations.

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Doping of ZnSe with gold results in the appearance of three broad emission bands which peak at 575 nm, 605 nm and 695 nm (at 2 K). In ODMR experiments each band gives rise both to shallow-donor and to deep-centre magnetic resonance transitions and each is thus identified as being due to donor-deep-centre recombination. The deep centre (Au-1) associated with the 605 nm band has orthorhombic symmetry with I&/ = 2.226, Ig,I = 2.156 and lgll = 1.950, where y is along a (110) direction and where x and z are tilted by 8" from (1 12) and (1 11) directions respectively. For the 695 nm band the deep centre (Au-2) is unusual in having axial symmetry about a (100) axis, with lgllI = 2.183, (g,l = 2.033, IA~I('~AU)I, c l 0 x cm-'. For the 575 nm band the deep centre (Au-3) is again orthorhombic, with lg,l = 2.002, Ig,(l00)1 = 2.010 and lgzl = 2.083, with the x and z axes tilted from (112) and (111) directions by 20". The Au-1 centre is ascribed to a gold-containing A centre, the Au-2 to interstitial gold in octahedral selenium coordination and the Au-3 to substitutional gold associated with a perturbing defect. cm-' and lA,(197A~)l = 24 x $ Now at