Photodissociation of formaldehyde in a molecular beam

Abstract

Formaldehyde photopredissociation was studied under collisionless conditions by the technique of crossed laser and molecular beams. Detection of the molecular product co after excitation of H2CO near the s1 origin gives strong support to the sequential coupling model for fast nonradiative decay of S1 states through broadened s 0 levels to the continuum. For H2CO excitation at 283.9 nm, formation of the radical product HCO dominates dissociation to molecular products by at least one order of magnitude.

Formaldehyde Photochemistry

“…Mole cular be am ti me-of-fl ig ht photofrag me nt spectr a by Ho et al (56) show that H2 + CO and H + HC O photofrag me nt s for m wi th in 3 f.is of S 1 photoe xcit ati on in the complete abse nce of coll i si ons. The se expe ri me nts pr ovi de important confir mati on of the colli si on-f ree S1 de cay me chani sm de scri be d in this re view.…”

“…For D2CO , the smalle r Sl -S o cou pl i ng ma tri x ele ments (2 9, 36, 39) and smalle r tu nneli ng ra te s (33) lea d to the primaril y radiative de ca y obse rved fo r the 4 0 and 4 1 le vels (47,58) as we ll as to the low photochem ic al quantum yi elds (20). Most of the en ergy re lea sed upon di ssocia ti on to H2 + CO (45-85%) (56) is fou nd in tra nsla tion. CO vi bra ti on accou nts for only ,...…”

“…A fu ll unde rsta ndi ng of the fo rce s among the atoms as the H2 is fo rme d and se pa ra te s from the CO re qui res fu rthe r expe ri me nt and compu ta ti on. For H + HC O fra gme n ta ti on near the threshol d, le ss than hal f of the en ergy is fou nd in vi brat ion (61) and transla ti on (56).…”

Cavity ring-down spectroscopic study of acetaldehyde photolysis in the gas phase, on aluminum surfaces, and on ice films

“…They can undergo photolysis or reactions in the gas phase and on the surface of the snowpack. Due to the crucial role played by aldehyde photolysis in the formation of HO x radicals in the atmosphere, the gas-phase photolysis of formaldehyde and acetaldehyde have been studied extensively [3][4][5][6]. Our group has previously studied the wavelength-dependent photolysis of propionaldehyde [7], n-butyraldehyde [8], i-butyraldehyde [8], n-pentanal [9], i-pentanal [10], t-pentanal [10], n-hexanal [11], and n-heptanal [11] in the gas phase, by using laser photolysis combined with cavity ring-down spectroscopy [12,13].…”

Photoelectron spectroscopy of the hydroxymethoxide anion, H2C(OH)O−

“…31 Here, a solid sample of polyoxymethylene (formaldehyde polymer) is heated to 60(5) °C under a 40 psig flow of argon. The principal product from the decomposition of polyoxymethylene is gaseous monomeric formaldehyde, but water and other small oligomers, such as dimeric formaldehyde and trioxane, are also formed.…”