Strong B(E1) transitions have been recently observed between states in the 180 nucleus which follow roughly the energy sequence of a dimolecular e + 14C rotator. These findings have been interpreted by Gai et al. as evidence for a molecular dipole degree of freedom being present in the 180 nucleus. However, this idea was contradicted by the results of a microscopic multichannel calculation performed by Descouvemont and Baye which was based on elastic e + ~4C and inelastic e + 14 C (2 +) many-body cluster wave functions. We have improved this study by performing a microscopic multichannel calculation including additionally a n + 170 many-body fragmentation in order to enlarge our model space by those shell model components which dominate the structure of the (positive parity) 180 ground state band. Like Descouvemont and Baye we find a positive parity e + 14C molecular band in 180 and, additionally, a rather strong collectivity in the lowest 1-, 3-, and 5-states in 180. However, since the internal structure is different within these states, the calculated states should not be interpreted as a negative parity e + 14C molecular band. In this perspective, the microscopic multichannel calculations do not support the hypothesis of a molecular dipole degree of freedom being present in the tsO nucleus.

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We have performed a study of the 140(a,p)17F reaction at stellar energies within the framework of the Generator Coordinate Method (GCM). Our calculation improves a previous study by enlargement of the model space.The mechanism of break-out from the hot CNO-cyele in novae and x-ray bursts, which subsequently leads to nucleosynthesis of elements up to the S~Ni region by rapid proton capture, is still an important problem in nuclear astrophysics [1]. Besides the 1sO (a,7) lONe re-140(2+) and p + 17F product states. The internal degrees of freedom of the a-cluster, the 140 ground state (140(0+)), the first excited 2 + state in 140 (140(2+)) and the ~7F ground state were all described by harmonic oscillator shell model states in jj-coupling. The relative wave functions between the various fragmentations have been determined from the coupled RGM-equations following along the lines of Res 3. The oscillator parameters for the cluster basis wave functions as weII as parameters in the nucleon-nucleon interaction were adjusted to reproduce the correct energy spUttkag between the proton channel and the a-channel as well as the energy positions of the two lSNe states close to the a-threshold (the 2 + state and the 3~ state at -24 keV). Our calculated lSNe level spectrum is shown in Fig. 1. Fig. 2 in terms of the astrophysical S-factor. Up to E < 300 keV, it is dominated by the tail of the 2 + resonance, exceeding the contribution arising from the high-energy wing of the 3~-bound state by about one order of magnitude. In the energy regime E g 0.3 -2.5 MeV the cross section is given by the contribution from the J = 1 partial wave which can be separated into a non-resonant direct transfer part and its interference with the 1-resonance at E = 3.6 MeV (not present in the previous study [3]). We find a constructive interference below the resonance energy. The 4 + resonance at 2.79 MeV yields an important contribution to the calculated S-factor at E = 2.7-3 MeV. There are experimentally known resonances in the a + 140 channel at E _> 1 The calculated transfer cross section is shown inMeV which are not present in our GCM study (see Fig. 1).The 140(a,p)l~F reaction rate can be derived at following the procedure discussed in Ref. 3. Comparing the present results to those of Ref. 3 we find the following conclusions which are important for the 140(a,p)l~F rate at astrophysical energies: i) The resonant contribution arising from the 2+ state is smaller in the present calculation by about a factor of 3.6. This can be traced back to a smaller a-width of this state, while its prcton-width Fp = ~ keV remains uneffected hy the inclusion of an a + 140(2+) configuration (experimental value P~ = 25 =k t0 keV). We now find F~ = 1.3 9 10 -~2 MeV which is in close agreement with the value deduced from the reduced a-width of its analogue-state in lsO (F~ = 1.1.5 9 10 -62 MeV, Ref.2). The reduction in the calculated a-width is caused by a stronger configuration mixing between the 2 + state with the 2 + state at -1.49MeV, whose energy splitting (and po...

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