Eric E. Mayer

Double-resonance spectroscopy of the high Rydberg states of HCO. III. Multiple pathways in the vibrational autoionization of the bending overtone

Ultraviolet first-photon absorption selects individual rotational levels in the Renner–Teller split (020) vibronic band system in the 3pπ 2Π Rydberg state of HCO. These gateway states serve as originating levels for vertical second-photon transitions to vibrationally autoionizing Rydberg series converging to individual rotational levels associated with the (0200) and (0220) states of HCO+. Linewidths of assigned series convey information on autoionization dynamics. Resonances throughout the (020) autoionization spectrum match sharp profiles seen earlier for series converging to HCO+(010). Linewidths for autoionization via relaxation both of the bending fundamental and its overtone are measurably narrower than resonances built on CO stretch, (001), which indicates that mode-selectivity inhibiting bending autoionization relative to stretch extends to the bending overtone. Features in the (020) spectrum that fall below the threshold energy for decay by autoionization to the (010) continuum appear with dimini...

Double-resonance spectroscopy of the high Rydberg states of HCO. I. A precise determination of the adiabatic ionization potential

We report the first spectroscopic observation of the high Rydberg states of HCO. Individual lines in a system of vibrationally autoionizing Rydberg series converging to the (010) state of HCO+ are rotationally labeled in a double‐resonance excitation scheme that uses resolved levels in the (010) A′ vibronic component of the 3pπ 2Π Rydberg state as intermediates. Observed high‐Rydberg structure extends from the adiabatic ionization threshold—which falls just below the principal quantum number of 12 in the vibrationally excited series—to the (010) vertical threshold. Elements of a single series extending from n=12 to 50, for which the total angular momentumless spin can be assigned as N=1, are extrapolated to obtain a vertical convergence limit with respect to the 3pπ 2Π(010)A′ N′=0 intermediate state of 20 296.9±0.3 cm−1. Referring this transition energy to the ground state, and subtracting the precisely known fundamental bending frequency of the cation, establishes the adiabatic ionization potential corre...

Double-resonance spectroscopy of the high Rydberg states of HCO. II. Mode specificity in the dynamics of vibrational autoionization via CO stretch versus bend

We report ionization-detected absorption spectra of vibrationally autoionizing high Rydberg states of formyl radical. Steps of uv–visible double resonance with selected rovibrational levels of the 3pπ 2Π Rydberg state of HCO promote Franck–Condon vertical transitions that isolate series converging to (010) (bend) and (001) (CO stretch) excited states of HCO+. Final state energies in these spectra exceed the threshold for production of the cation ground state. Intensities and linewidths of observed resonances convey information on the dynamics of electron ejection driven by the vibronic relaxation of specific normal modes of the linear triatomic core. Many resonances in (010) and (001) autoionization spectra exhibit widths that approach the resolution of our laser. Other resonances in series converging to both limits are noticeably broadened, with linewidths that display an inverse cubic dependence on principal quantum number. Among these broader resonances, those in series that decay by relaxation of CO s...

Double-resonance spectroscopy of the high Rydberg states of HCO. V. Rovibronic interactions and l-uncoupling in the (010) manifold

We report the ionization-detected absorption spectra of autoionizing Rydberg states converging to the (010) vibrational level of HCO+. Sharp second-photon resonances appear in transitions from first-photon-prepared originating states that have total angular momentum (less-spin) from N′=0 to 5, selected from the Σ+ and Σ− components of the (010) band of the 3pπ2Π Rydberg state. We systematically compare spectra in order to characterize observed resonances in terms of the good total angular momentum quantum number, N. Rydberg analysis establishes the convergence of series to detailed cation-core rotational quantum numbers, N+. Observed series are found to fit well with simulations employing a limited set of constant quantum defects (δ=1.062, 0.794, 0.606, 0.253, 0.015, 0.002, −0.027 and −0.076). The strengths of observed transitions as a function of initial and final total angular momentum provide a purely experimental indication of the appropriate assignment of the approximately good orbital angular moment...

State–to–state dynamics in the high Rydberg states of polyatomic molecules

Rydberg states in polyatomic molecules exhibit dynamics that bear on issues of longstanding importance for theory. Coupling is made complicated, however, by the presence of many rovibrational degrees of freedom and the existence of multiple pathways for intramolecular relaxation. In work on vibrationally autoionizing states of HCO and NO2, we have applied multiple resonance excitation strategies to isolate single rovibrational Rydberg–Rydberg transitions, the positions, lineshapes and intensities of which reflect coupling strengths for state–detailed relaxation processes.