The dominant nova nucleosynthetic path followed by the thermonuclear runaway on the surface of the white dwarf is very sensitive to the chemical composition of the white dwarf, the extent to which the convective mixing occurs, and the thermal history of the envelope. Such details can be partially obtained via the laboratory analysis of the Si isotopic abundance ratios (²⁹Si/²⁸Si and ³⁰Si/²⁸Si) in presolar grains of nova origin. To estimate the Si isotopic abundances in presolar grains, it is critical to know the rates of the thermonuclear reactions which affect the Si production and destruction in novae. Two such reactions are ²⁹P(p,γ)³⁰S and ³⁰P(p,γ)³¹S. The ³⁰P(p,γ)³¹S reaction rate also plays an important role in understanding how the nova nucleosynthetic path is shifted to the A > 30 mass region. At nova temperature range (0.1 ¨C 0.4 GK), the ²⁹P(p, γ)³⁰S reaction rate is thought to be dominated by two low energy proton-unbound 3⁺ and 2⁺ resonances, whose properties were mostly unknown until the present work; while the ³⁰P(p, γ)³¹S reaction rate is dominated by the resonances corresponding to the excitation energies in the range of 6 ¨C 7 MeV in ³¹S. Despite recent progress in determining the properties of the ³¹S resonances, some of the known states lack firm spin-parity assignments, and the existence of unobserved resonances cannot yet be precluded. We investigated the level structure of ³⁰S via the ³²S(p,t)³⁰S and ²⁸Si(³He,nγ)³⁰S reactions and that of ³¹S via the ³²S(p,d)³¹S reaction. In my talk, I will discuss these experiments and their results, and present astrophysical implications.

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