We study the first excited state of He4 in a microscopic {H3+p,He3+n} cluster
model, including H3 and He3 distortions. The phenomenological 1S0 H3+p
scattering phase shift is well reproduced. We localize a complex pole of the
S-matrix between the H3+p and He3+n thresholds. The corresponding resonance
parameters are E_r=93 keV position relative to H3+p, and Gamma=390 keV width. A
pole search is also performed in an extended R-matrix method, and a resonance
is found with parameters E_r=114 keV and Gamma=392 keV. The R-matrix approach
gives several additional poles, some of which may be connected with an enhanced
threshold effect.Comment: 13 pages, 2 figure