Photodissociation Dynamics of Benzaldehyde (C₆H₅CHO) at 266, 248, and 193 nm

Abstract

The photodissociation of gaseous benzaldehyde (C(6)H(5)CHO) at 193, 248, and 266 nm using multimass ion imaging and step-scan time-resolved Fourier-transform infrared emission techniques is investigated. We also characterize the potential energies with the CCSD(T)/6-311+G(3df,2p) method and predict the branching ratios for various channels of dissociation. Upon photolysis at 248 and 266 nm, two major channels for formation of HCO and CO, with relative branching of 0.37:0.63 and 0.20:0.80, respectively, are observed. The C(6)H(5)+HCO channel has two components with large and small recoil velocities; the rapid component with average translational energy of approximately 25 kJ mol(-1) dominates. The C(6)H(6)+CO channel has a similar distribution of translational energy for these two components. IR emission from internally excited C(6)H(5)CHO, ν(3) (v=1) of HCO, and levels v≤2, J≤43 of CO are observed; the latter has an average rotational energy of approximately 13 kJ mol(-1) and vibrational energy of approximately 6 kJ mol(-1). Upon photolysis at 193 nm, similar distributions of energy are observed, except that the C(6)H(5)+HCO channel becomes the only major channel with a branching ratio of 0.82±0.10 and an increased proportion of the slow component; IR emission from levels ν(1) (v=1) and ν(3) (v=1 and 2) of HCO and v≤2, J≤43 of CO are observed; the latter has an average energy similar to that observed in photolysis at 248 nm. The observed product yields at different dissociation energies are compared to statistical-theory predicted results based on the computed singlet and triplet potential-energy surfaces.

Derivative couplings between TDDFT excited states obtained by direct differentiation in the Tamm-Dancoff approximation

“…[65][66][67][68][69][70][71][72][73][74] A great deal of theory and experiment has focused on the two lowest triplet states of benzaldehyde in order to explain the mechanism of the molecule's highly phosphorescent radiation. 65,66,71,[73][74][75][76][77] The interstate mixing between the T 1 (n-π *) and T 2 (π -π *) states of benzaldehyde was estimated as long ago as the 1970s.…”

Using heavy atom rare gas matrix to control the reactivity of 4-methoxybenzaldehyde: A comparison with benzaldehyde

“…The observed decarbonylation of p-anisaldehyde in a xenon matrix, leading to anisole + CO (see Scheme 2), could indeed be expected to occur under the used experimental conditions, considering that photodecarbonylation is a common process in aldehydes, both aliphatic and aromatic. 23,24,[42][43][44][45][46][47][48][49][50] In the spectrum of photolysed p-anisaldehyde isolated in solid xenon, a few new low intensity bands not ascribable to anisole were also observed. These appeared at 1636, 1759/1756, 1578/1577, 1493/1491, 1448/1446, 1322, 1139, 847, 840, 645, and 610 cm −1 .…”

Conditions and Probability of electron-Photon Interactions

“…Other examples are in biology and chemistry. For example in biology the DNA cells [22], in chemistry the benzaldehyde [23] compounds have UV photosensitivity at wavelengths around 250 nm. In general: these molecules are photosensitive at a specific wavelength and in its close vicinity.…”