The Cases

The identified cases are described in the following section; some examples are given below. It should be noted that the rovibronic states of different electronic states of a molecule may be described using different cases. For example, the ground, X^2\Pi electronic state of NO may be described within the hunda case whereas the excited, A^2\Sigma^+ electronic state would be better described using the hundb case. The electronic state is identified by its single-letter spectroscopic symbol (X, A, a, B, etc.) There follows a list of the cases identified in version 0.3 of XSAMS with some examples:

0. General case for arbitrary quantum numbers and symmetry (gen)
1. Diatomic closed shell (dcs): CO, N_2, NO^+
2. Hund’s case (a) diatomics (hunda): NO, OH [for low J]
3. Hund’s case (b) diatomics (hundb): O_2, OH [for high J]
4. Closed-shell, linear triatomic molecules (ltcs): CO_2, HCN
5. Closed-shell, non-linear triatomic molecules (nltcs): H_2O
6. Closed-shell, symmetric top molecules (stcs): NH_3, CH_3Cl
7. Closed-shell, linear, polyatomic molecules (lpcs): C_2H_2
8. Closed-shell, asymmetric top molecules (asymcs): C_2H_4
9. Open-shell, asymmetric top molecules (asymos): CH_3O
10. Closed-shell, spherical top molecules (sphcs): CH_4, SF_6
11. Open-shell, spherical top molecules (sphos)
12. Open-shell, linear triatomic molecules (ltos): CCH
13. Open-shell, linear, polyatomic molecules (lpos): C_3H, C_{10}H
14. Open-shell, non-linear triatomic molecules (nltos): HO_2, CH_2