Table 2.
General assignment of bands present in the 3800−1800 cm−1 range of the IR spectra of Cit−HA−4 h, Cit−HA−24 h; Cit−HA−96 h in contact with 20 mbar of H2O, after 60 min outgassing at b.t., and after exchange with D2O and subsequent outgassing at b.t.
| Band position (cm−1) | Assignment28, 29 |
|---|---|
| 3750−2500 (range) | Stretching modes of adsorbed H2O, bulk and surface hydroxy groups (e.g., of HPO4 2−) involved in H-bonding |
| 3570 (maximum) | Stretching mode of bulk OH−, occupying the 4e position in the hexagonal lattice (so-called “columnar OH”, since they are aligned in columns parallel to the c-axis) |
| 2750−2000 (range) | Stretching modes of adsorbed D2O, and surface −OD groups involved in D-bonding |
| 2635 (maximum) | Stretching mode of bulk “columnar” OD− |
| 2200−1800 (range) | Combination modes of fundamental phosphate bulk absorption (falling below the transparency limit in the adopted experimental conditions) |