The Rydberg spectroscopy of the formyl radical and the spectroscopic characterization of the vibrational force field of formyl cation

Krista Prentice, Purdue University


The purpose of this investigation was to establish an excitation pathway which accessed high-lying, Rydberg series that converged to rovibrational states in the 1Σ+ electronic state of HCO+. Through the 3 p π 2Π Rydberg intermediate state, we observe, using double-resonance spectroscopy, Rydberg series converging to the ion. Using the output of a frequency-tripled, pulsed dye laser, we have extended the ionization-detected one-photon absorption spectrum of HCO to include higher excited vibronic levels of the 3 p π 2Π Rydberg state in the interval from 47 900 to 50 500 cm−1. Included in this spectrum are band systems associated with bending overtones from (030) through (060), as well as cold-band transitions to bend-CO-stretch combinations from (011) through (031). The use of a separate, synchronized, fixed-frequency visible ionization pulse, in a technique that we term assisted REMPI, reveals a number of weak features. We find sequence-band transitions to confirmed states as well as to the higher excited levels, (041) and (070), which fall out of range as cold bands. We find a very weak structure that we assign to the (100)-(000) transition terminating on the CH-stretch fundamental. This band appears in the 3 p π state at a frequency very close to the value found for ω1 in the HCO+ cation. Continuing a trend established in earlier observations, we find that the Renner-Teller coupling of the electronic orbitial and vibrational angular momentum in the 3 p π 2Π state of HCO varies with bending quantum number, decreasing linearly with v2 in both fundamental as well as bend-CO-stretch combination states. Photoselecting individual vibrational-rotational levels in the intermediate 3 p π 2Π state, allow us to utilize double resonance to study high-Rydberg series converging to various vibrationally excited states of HCO+. We report precise thresholds for the (040), (050), (060), and (070) states of HCO+ and determine the spectroscopic constants ω2, χ22, and g 22. In addition, we determined the anharmonicity associated with CO-stretch (χ23) based on experimentally resolved precise thresholds for the (011) and (031) states of the cation.




Grant, Purdue University.

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