State-selective photodissociation dynamics of formaldehyde: Near threshold studies of the H+HCO product channel
- Department of Chemistry, Queen's University, Kingston, Ontario K7L 3N6 (Canada)
The laser-induced photodissociation of formaldehyde in the wavelength range 309<{lambda}<330 nm has been investigated using H (Rydberg) atom photofragment translational spectroscopy. Photolysis wavelengths corresponding to specific rovibronic transitions in the A(tilde sign) {sup 1}A{sub 2}(leftarrow)X(tilde sign) {sup 1}A{sub 1} 2{sub 0}{sup 1}4{sub 0}{sup 3}, 2{sub 0}{sup 2}4{sub 0}{sup 1}, 2{sub 0}{sup 2}4{sub 0}{sup 3}, 2{sub 0}{sup 3}4{sub 0}{sup 1}, and 2{sub 0}{sup 1}5{sub 0}{sup 1} bands of H{sub 2}CO were studied. The total kinetic energy release spectra so derived can be used to determine partial rotational state population distributions of the HCO cofragment. HCO product state distributions have been derived following the population of various different N{sub K{sub a}} levels in the A(tilde sign) {sup 1}A{sub 2} 2{sup 2}4{sup 3} and 2{sup 3}4{sup 1} states. Two distinct spectral signatures are identified, suggesting competition between dissociation pathways involving the X(tilde sign) {sup 1}A{sub 1} and the a(tilde sign) {sup 3}A{sub 2} potential energy surfaces. Most rovibrational states of H{sub 2}CO(A(tilde sign) {sup 1}A{sub 2}) investigated in this work produceH+HCO(X(tilde sign) {sup 2}A{sup '}) photofragments with a broad kinetic energy distribution and significant population in high energy rotational states of HCO. Photodissociation via the A(tilde sign) {sup 1}A{sub 2} 2{sup 2}4{sup 3} 1{sub 1,1} (and 1{sub 1,0}) rovibronic states yields predominantly HCO fragments with low internal energy, a signature that these rovibronic levels are perturbed by the a(tilde sign) {sup 3}A{sub 2} state. The results also suggest the need for further careful measurements of the H+HCO quantum yield from H{sub 2}CO photolysis at energies approaching, and above, the barrier to C-H bond fission on the a(tilde sign) {sup 3}A{sub 2} potential energy surface.
- OSTI ID:
- 20991303
- Journal Information:
- Journal of Chemical Physics, Vol. 127, Issue 6; Other Information: DOI: 10.1063/1.2752160; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0021-9606
- Country of Publication:
- United States
- Language:
- English
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