Photoelectron spectrum of NO

The general selection rule is, when both the initial molecular and final ion states are in case (a)  

Additional selection rules for homonuclear molecules are specified in Xie and Zare (1990). The selection rule for parity can be understood as follows  

The total parity of the final state is equal to the parity of the ionic level times the parity of the electron partial wave (which is even for even l and odd for odd l). For example, for a transition from a 1E+ molecular state to a 2II ion state, starting from J = 4 (e-level, + parity), the J+ = 7/2 rotational level of the ion has two components one e-level (— parity), one /-level (+ parity) (see Fig. 8.16). The selection rule for allowed one-photon transitions is H— —. Consequently, for the transition into the ion e-level, the partial wave of the ejected electron is l = 0 (s) for the transition into the ionic /-level, the partial wave of the ejected electron is l = 1 (p). Equation (8.1.8a), with S -1- = 1/2, is satisfied for these l values. 

The usual rotational branch notation in PES is that the branches corresponding to N+ — N or J+ — J transitions are named in the same way as the usual rotational branches AN = 0 Q-branch AN — 1, /2-branch and AN = — 1, P-branch. 

However, when the PES transition is between molecular and ion states which belong to different Hund s cases, then the rotational branches are often labeled according to the numerical value of the change in pattern-forming rotational quantum number (respectively J,N,J,N+, and J+ for Hund s cases (a), (b), (c), (d), and (e)), which can have either integer or half-integer value. 

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Question. Which low-lying states of NO would you expect to feature in the He I ultraviolet photoelectron spectrum of NO (Consider removal of an electron from only the three outermost orbitals of NO.) Indicate whether a long or short vibrational progression would be anticipated in each case. 

Figure 12. Comparison of the photoelectron spectrum of NO with the original ZEKE spectrum of the first band, with demonstration of rotational resolution of the ion state.

Figure 8.3 Photoelectron spectrum of NO obtained by resonant one-photon excitation of N = 21 of the A2E+(u = 0) state (from Wilson et al., 1984).

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