According to the extended-Gruneisen function, one can infer immediately that the skin H-O bond is shorter than those inside the bulk. Quantum computations confirmed that the skin H-O bond is 8% shorter and the local density is 25% lesser than the bulk reference at 377 K. XPS measurements suggested that surface O-O distance is 5.9% longer than the bulk reference 2.8 Å . Fig. shows the PDPS profiled for the sized droplets of (5%D + 95%H) water focusing on the D-O vibration. The PDPS peak area resolves the fraction of the skin phonon abundance transiting from the mode of ordinary water, which is droplet size dependent (Fig. ). Given the volume of a sphere, V ∝ R 3 , one can derive the skin volume ratio F(R) of the sphere, the shell thickness and the skin H/D-O bond length. Equaling the F(R) to the skin volume ratio, one can obtain, ∆Vskin/V = ∆Nskin/N = 3∆Rskin/R. The ∆Rskin = F(R)R/3 = 0.9dH = 0.90 Å is the H/D-O length in the skin, which is 10% shorter than the standard, corresponds to a 3.0 Å thick of the outermost O:H-O layer, according to the HBCP formulation in Table . The skin layer may extend gradually inward, but the PDPS only distills the outermost one, which would be sufficient to distinguish the skin identity. a) The ωH transits from 3150/3200 cm -1 for bulk ice/water to their common supersolid skin mode of 3450 cm -1 . (b) Core-shell resolved ωDO peaks and (c) the fraction F(R) of skin phonon populations . (H2O)N cluster size dependency of the (d) O:H-O segmental length, (e) vibration frequency (Exp ), and (f) force constant (bond stiffness) .