| Zn-content (x) | υ’ cm−1 | υ1 cm−1 | υ2 cm−1 | υ3 cm−1 | υ4 cm−1 | υ5 cm−1 |
| 0.0 | 783 | 550 | 409 | 383 | 261 | 223 |
| 0.1 | 793 | 550 | 407 | 380 | 284 | 223 |
| 0.2 | 795 | 547 | 411 | 381 | 268 | 224 |
| 0.3 | 795 | 549 | 410 | 386 | 273 | 226 |
| 0.4 | 799 | 551 | 423 | 380 | 269 | 219 |
| 0.5 | 795 | 555 | 430 | 387 | 255 | 215 |