Photoabsorption in formaldehyde: Intensities and assignments in the discrete and continuous spectral intervals
Theoretical investigations of total and partial-channel photoabsorption cross sections in molecular formaldehyde are reported employing Stieltjes--Tchebycheff (S--T) technique and separated-channel static-exchange (IVO) calculations. Vertical one-electron dipole spectra for the 2b/sub 2/(n), 1b/sub 1/(..pi..), 5a/sub 1/(sigma), 1b/sub 2/, and 4a/sub 1/ canonical molecular orbitals are obtained using Hartree--Fock frozen-core functions and large basis sets of compact and diffuse normalizable Gaussians to describe the photoexcited and ejected electrons. Calculated discrete excitation spectra provide reliable zeroth-order approximations to both valence and Rydberg transitions; in particular, the 2b/sub 2/(n) ..-->..nsa/sub 1/, npa/sub 1/, npb/sub 2/, and nda/sub 2/ IVO spectra are in excellent accord with recent experimental assignments. Convergent (S--T) photoionization cross sections in the static-exchange (IVO) approximation are obtained for the 15 individual partial channels associated with ionization of the five occupied molecular orbitals considered. Resonance features in many of the individual-channel photoionization cross sections are attributed to contributions from valencelike a/sub 1/sigma* (CO), a/sub 1/sigma* (CH), and b/sub 2/sigma* (CH)/..pi../sub y/* (CO) molecular orbitals that appear in the photoionization continua. The vertical electronic cross sections for /sup 1/A/sub 1/..-->../sup 1/B/sub 1/, /sup 1/B/sub 2/, and /sup 1/A/sub 1/ excitations are in generally good accord with previously reported CI (S--T) predictions of continuum orbital assignments and intensities, although some discrepancies due to basis-set differences are present in the /sup 1/B/sub 1/ and /sup 1/B/sub 2/ components, and larger discrepancies apparently due to channel coupling are present in the /sup 1/A/sub 1/..-->../sup 1/A/sub 1/ cross section. Partial-channel vertical electronic cross sections for the production of the five lowest parent-ion electronic states are found to be in general agreement with very recent photoelectron branching-ratio measurements.
- Research Organization:
- Department of Chemistry, Indiana University, Bloomington, Indiana 47401
- OSTI ID:
- 6509913
- Journal Information:
- J. Chem. Phys.; (United States), Vol. 69:10
- Country of Publication:
- United States
- Language:
- English
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