Investigating the physical mechanisms driving the dynamical evolution of young star clusters is fundamental to our understanding of the star formation process and the properties of the Galactic field stars .
The young ( \sim 2 Myr ) and partially embedded cluster Chamaeleon I is one of the closest laboratories to study the early stages of star cluster dynamics in a low-density environment .
The aim of this work is to study the structural and kinematical properties of this cluster combining parameters from the high-resolution spectroscopic observations of the Gaia-ESO Survey with data from the literature .
Our main result is the evidence of a large discrepancy between the velocity dispersion ( \sigma _ { stars } = 1.14 \pm 0.35 ~ { } km~ { } s ^ { -1 } ) of the stellar population and the dispersion of the pre-stellar cores ( \sim 0.3 ~ { } km~ { } s ^ { -1 } ) derived from submillimeter observations .
The origin of this discrepancy , which has been observed in other young star clusters is not clear .
It has been suggested that it may be due to either the effect of the magnetic field on the protostars and the filaments , or to the dynamical evolution of stars driven by two-body interactions .
Furthermore , the analysis of the kinematic properties of the stellar population put in evidence a significant velocity shift ( \sim 1 ~ { } km~ { } s ^ { -1 } ) between the two sub-clusters located around the North and South main clouds of the cluster .
This result further supports a scenario , where clusters form from the evolution of multiple substructures rather than from a monolithic collapse .

Using three independent spectroscopic indicators ( the gravity indicator \gamma , the equivalent width of the Li line at 6708 Å , and the H \alpha 10 % width ) , we performed a new membership selection .
We found six new cluster members all located in the outer region of the cluster , proving that Chamaeleon I is probably more extended than previously thought .
Starting from the positions and masses of the cluster members , we derived the level of substructure Q , the surface density \Sigma and the level of mass segregation \Lambda _ { MSR } of the cluster .
The comparison between these structural properties and the results of N-body simulations suggests that the cluster formed in a low density environment , in virial equilibrium or supervirial , and highly substructured .