We have investigated the femtosecond
laser-induced fragmentation
of C2H2
q
ion beam
targets in various initial configurations, including acetylene (linear
HCCH), vinylidene (H2CC), and cis/trans. The initial configuration is shown to have a tremendous
impact on the branching ratio of acetylene-like (CH
q
1
+ CH
q
2
)
and vinylidene-like (C
q
1′ + CH2
q
2′) dissociation of a specific C2H2
q
molecular ion. In particular, whereas C2H2
+ generated from C2H2, a linear HCCH target, exhibits comparable levels of acetylene-like
and vinylidene-like fragmentation, vinylidene or cis/trans configuration ion beams preferably undergo
vinylidene-like fragmentation, with an acetylene branching ratio ranging
from 13.9% to zero.