Consideration of the non-torsional C1-H/D/T BCPs is presented inFigure 3 , Table 2(c) and Table 2(d) . For HD glycine the values of T_σ, F_σ and A_σ are all slightly larger for C1-D3 BCP (the R_a stereoisomer) than for the corresponding T_σ, F_σ and A_σ values of C1-H3 BCP (the S_a stereoisomer), seeTable 2(c) . The same correspondence is found for the C1-D10BCP. This does not hold for the HT glycine where the opposite effect is found for the C1-T10 BCP , where all three of the T_σ, F_σ and A_σ values are smaller for the C1-T10 BCP compared with the C1-H10 BCP . A mixed effect is found for the dominance of the T_σ, F_σ and A_σ values of the C1-T3 BCPcompared with the C1-H3 BCP . Particularly high values of the F_σ and A_σ are observed for the O5-H6BCP and the C2-O5 BCP that reduce significantly with the addition of the T isotope to X3 and X10 sites. Despite the remotely positioned location of the C2-O5 BCP and O5-H6 BCP from the site of the D and T substitutions, the effect of the T isotope in particular is apparent where a significant reduction of the T_σ, F_σ and A_σ values of both the C2-O5 BCP and O5-H6 BCP compared with D and T, see Table 2(d) . These observations are relevant for the interpretation of the vibrational mode coupling, which affects both IR and CD spectra. This is because the high values of F_σ and A_σ of both the C2-O5 BCPand O5-H6 BCP that are consistent with the C2-O5-H6 undergoing a bending vibration which is coupled to the methylene group wagging which is thus expected to be preserved upon deuteration at C1. Thelowering of the corresponding values of F_σ and A_σ for the T isotope indicates that the C2-O5-H6 bending vibration is uncoupled from that of C1-HT wagging.