Determination of the singlet/triplet branching ratio in the photodissociation of ketene

Journal Article · Fri Feb 01 00:00:00 EST 1991 · Journal of Chemical Physics; (USA)

DOI:https://doi.org/10.1063/1.459917· OSTI ID:6170347

Kim, S K; Choi, Y S; Pibel, C D; Zheng, Q; Moore, C B ^[1]

---

1. Department of Chemistry, University of California, Berkeley and Materials and Chemical Sciences Division of the Lawrence Berkeley Laboratory, Berkeley, California 94720 (US)

The rotational distributions of CO products from the dissociation of ketene at photolysis energies 10 cm{sup {minus}1} below, 56, 110, 200, 325, 425, 1107, 1435, 1720, and 2500 cm{sup {minus}1} above the singlet threshold (30 116.2 cm{sup {minus}1} ), are measured in a supersonic free jet of ketene. The CO({ital v}{double prime}=0) rotational distributions at 56, 110, 200, 325, and 425 cm{sup {minus}1} are bimodal. The peaks at low {ital J}{prime}s, which are due to CO from the singlet channel, show that the product rotational distribution of CO product from ketene dissociation on the singlet surface is well described by phase space theory (PST). For CO({ital v}{double prime}=0) rotational distributions at higher excess energies (1107, 1435, 1720, and 2500 cm{sup {minus}1} ), the singlet and triplet contributions are not clearly resolved, and the singlet/triplet branching ratios are estimated by assuming that PST accurately predicts the CO rotational distribution from the singlet channel and that the distribution from the triplet channel changes little from that at 10 cm{sup {minus}1} below the singlet threshold. The singlet yield shows a rapid increase in the low excess energy region (0--300 cm{sup {minus}1} ), and a slower increase above. The singlet and triplet rate constants are derived from the directly measured total rate constants using the singlet yields. The triplet rate constant increases monotonically with increasing photolysis energy through the singlet threshold region. The singlet rate constant is accurately established in the threshold region and found to increase much less rapidly than predicted by phase space theory. At 2500 cm{sup {minus}1} excess energy, the CO({ital v}{double prime}=1) rotational distribution is obtained, and the ratio of CO({ital v}{double prime}=1) to CO({ital v}{double prime}=0) products for the singlet channel is measured to be 0.045{plus minus}0.017.

• DOE Contract Number: AC03-76SF00098
• OSTI ID: 6170347
• Journal Information: Journal of Chemical Physics; (USA), Vol. 94:3; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
CARBON MONOXIDE
CHEMICAL REACTION YIELD
ROTATIONAL STATES
KETENES
PHOTOLYSIS
BRANCHING RATIO
CHEMICAL REACTION KINETICS
DISTRIBUTION
ENERGY-LEVEL DENSITY
CARBON COMPOUNDS
CARBON OXIDES
CHALCOGENIDES
CHEMICAL REACTIONS
DECOMPOSITION
ENERGY LEVELS
EXCITED STATES
KINETICS
ORGANIC COMPOUNDS
ORGANIC OXYGEN COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PHOTOCHEMICAL REACTIONS
REACTION KINETICS
YIELDS
400500* - Photochemistry