Neutron vibrational spectroscopic evidence for short H∙∙∙H contacts in the RNiInH1.4; 1.6 (R = Ce, La) metal hydride

•Close H–H contacts are realized in RNiInHx (R = Ce, x = 1.4; R = La, x = 1.6).•The H–H contacts violate the Switendick-Westlake criterion.•Neutron vibrational spectroscopic measurements probe the close H-H contacts.•Density functional theory calculations enable detailed analysis of the NVS data.•The spectroscopic signature for close H-H contacts in a metal hydride is reported.