Explicit expressions for the parity-violating s-wave and the
parity-conserving p-wave contributions to pi- weak-decay rates of Lambda
hypernuclei in the 1p shell are given in the weak-coupling limit, to update
previous shell-model calculations and to compare with recent pi- spectra and
total decay rates measured by the FINUDA Collaboration. A useful sum rule for
the summed strength of Lambda_{1s} --> pi- + proton_{1p} weak decays is
derived. Fair agreement between experiment and calculations is reached, using
the primary s-wave amplitude and Cohen-Kurath nuclear wavefunctions. The role
of the p-wave amplitude is studied in detail for Lambda-15N and found to be
secondary. Previous assignments of ground-state spin-parity values are
confirmed and a new assignment is made, spin-parity 3/2+ for Lambda-15N, based
on the substantial suppression calculated here for spin-parity 1/2+.Comment: published version; new footnote 2 added in proof; related to recent
FINUDA data, arXiv:0905.0623 [nucl-ex] submitted to Phys. Lett.