INTERFERENCE EFFECTS IN THE (2+1) PHOTON IONIZATION SPECTRUM OF THE HAND H' RYDBERG STATES OF NO

The (2 + 1) photon ionization spectrum of NO via the H-2 Sigma(+), 3d sigma and H'(II)-I-2, 3d pi (v = 0) Rydberg states has been recorded i n the UV range between 317.7 and 320 nm. The rotational analysis and t he Line intensity calculation have been performed by using a propensit y rule approach including the dominant contribution from the intermedi ate quasi-resonant (CII)-I-2 and D-2 Sigma(+) states (v = 0) to the tw o-photon transition moment. The line positions have been taken from th e upper stares and ground state rotational term values extracted from earlier absorption data. The calculations include l-mixing between the do and s sigma Rydberg states as well as l-uncoupling between the clo se lying d sigma and d pi components. In addition to the interference effects due to the mixing of the upper levels, a new type of interfere nce occurs in the two-photon transition amplitude through the two diff erent pathways via the C and D states. The mixing coefficients for the upper levels and the oscillator strengths for the C-X, D-X, H,H'-C, a nd H,H'-D transitions have been taken from the literature. Therefore, our calculation has been performed without any fitting of the molecula r parameters. The resulting simulated two-photon spectrum agrees reaso nably well with the observed one. This approach has been applied to re investigate a recently published analysis of the same system involving v = 1 in the upper states. We propose a completely revised analysis o f this (1,0) two-photon band, showing a very good agreement between ob served and calculated rotational profiles. This work demonstrates the ability of the propensity rule model for predictions of upper state ro tational and parity relative populations in multiphoton excitation exp eriments. These predictions may be essential when these upper levels a re used as intermediate levels for two-color experiments toward highly excited states or the ionization continuum.