| Approximation Option | a, eV−1 | b | R2 | *1, eV−1 | *2 | Ecr, eV*3 |
| 1 | −0.639 | 5.04 | 0.824 | −1.471 | 108,930 | 7.88 |
| 2 | −0.469 | 3.44 | 0.824 | −1.079 | 2763 | 7.34 |
| 3 | −0.317 | 2.02 | 0.824 | −0.731 | 105.69 | 6.38 |
| [13] [14] [27] |
|
| 0.526 | −1,139 | 3043 | 7.04 |