Far infra-red spectroscopy of La2-xSrxCuO4, 0.03 less than or equal to
x less than or equal to 0.24, compounds show weak phonon softening at
100-150 K in underdoped samples and, at a slightly lower temperature,
in 0.15 and 0.17 Sr LSCO. The maximum phonon renormalisation is 0.1%
which is much weaker than 1% as observed in YBCO compounds. Assuming t
hat the phonon renormalisations is LSCO and in YBCO have the same orig
in we conclude that (a) the correlation of phonon anomalies and local
lattice distortions with the opening of a spin gap should be reconside
red, and (b) if magnetic excitations do drive the above phenomena then
a spin gap should also exist in LSCO.