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Abstract. The angular motion of a few-body system is described with global vectors which depend on the positions of the particles. The previous study using a single global vector is extended to make it possible to describe both natural and unnatural parity states. Numerical examples include three-and four-nucleon systems interacting via nucleon-nucleon potentials of AV8 type and a 3α system with a nonlocal αα potential. The results using the explicitly correlated Gaussian basis with the global vectors are shown to be in good agreement with those of other methods. A unique role of the unnatural parity component, caused by the tensor force, is clarified in the 0 − 1 state of 4 He. Twoparticle correlation function is calculated in the coordinate and momentum spaces to show different characteristics of the interactions employed.

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t+t clustering in He isotopes is investigated by using two theoretical approaches. A role of the t+t cluster component in the ground state is examined with AMD triple-S, allowing the wider configuration space containing simultaneously the "t+t+valence neutrons" structure and "4 He +valence neutrons" structure. We understand the importance of the t + t component even for the ground state. Further, t + t resonances are investigated with RGM type approach. We obtained many t + t states as resonances near to t + t threshold.

The structure of the mirror nuclei 9 Be and 9 B is studied in a microscopic ␣ϩ␣ϩn and ␣ϩ␣ϩp threecluster model using a fully antisymmetrized nine-nucleon wave function. The two-nucleon interaction includes central and spin-orbit components together with the Coulomb potential. The ground state of 9 Be is obtained accurately with the stochastic variational method, while several particle-unbound states of both 9 Be and 9 B are investigated with the complex scaling method. The calculation for 9 Be supports the recent identification for the existence of two broad states around 6.5 MeV, and predicts the 3/2 2 Ϫ and 5/2 2 Ϫ states at about 4.5 MeV and 8MeV, respectively. The similarity of the calculated spectra of 9 Be and 9 B enables one to identify unknown spins and parities of the 9 B states. Available data on electromagnetic moments and elastic electron scatterings are reproduced very well. The enhancement of the E1 transition of the first excited state in 9 Be is well accounted for. The calculated density of 9 Be is found to reproduce the reaction cross section on a carbon target. The analysis of the beta decay of 9 Li to 9 Be clearly shows that the wave function of 9 Be must contain a small component that cannot be described by the simple ␣ϩ␣ϩn model. This small component can be well accounted for by extending a configuration space to include the distortion of the ␣ particle to tϩ p and hϩn partitions. ͓S0556-2813͑96͒02607-6͔