A microscopic study of the H 2 (d, γ) 4 He reaction with deuteron and He 4 bound state wave functions which include the D-state components is presented. Cross section and tensor analyzing powers are calculated for deuteron energies between 1 and 15 MeV. Deuteron D-state effects are found to be particularly important in the transition amplitude arising from the S 2 5 scattering state. A detailed comparison between cluster and microscopic calculations is presented. Using an effective two-body model the analysis of A yy data, in the energy range 1≤ E d≤ 15 MeV, gives for the asymptotic D/S state ratio in He 4 the value ρ=-0.18.