Higher Vibrationally Excited Levels of the 3pπ 2Π Rydberg State of HCO.

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 3pπ 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 3pπ 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 orbital and vibrational angular momentum in the 3pπ 2Π state of HCO varies with bending quantum number, decreasing linearly with v2 in both fundamental as well as bend-CO-stretch combination states. [ABSTRACT FROM AUTHOR]