Photodissociation of Methane at Lyman Alpha (121.6 nm)

Abstract

Laser induced fluorescence studies of hydrogen atom using four wave mixing technique are reported for the photodissociation of CH4 and its isotopomers at Lyα (121.6 nm). The source of dissociating and probe radiation is one and the same (delay time ≤ 20 nsec). The average translational energy of ejected hydrogen atoms (50 Kcal/mol) reveals that CH4 + hν → CH3 + H(

Unraveling the Photodissociation Branching and Pathways of Methane at 118 nm by Imaging the CH3, CH2, and CH Fragments

“…14,38,39 More recent studies under collision-free conditions resulted in much lower yields. By referencing to another molecule with known quantum yield, the reported results are 0.47 ± 0.11, 16 0.45 ± 0.10, 19 and 0.31 ± 0.05, 17 respectively. Alternatively, once all product channel branching fractions are determined, absolute yield Φ H can be deduced.…”

“…Following optical excitation to CH 4 (S 1 ), numerous fragmentation channels are energetically allowed, as listed below, where Δ H denotes the maximal available energy for disposal upon photolysis at 118 nm (10.48 eV photon energy). − To date, experimental investigations have mostly focused on detecting the H atom and/or H 2 fragments. − As such, the determinations of the channel branching were hampered by the complication that the probed H- and H 2 -fragments can originate from several distinct fragmentation channels; see the list. Yet, the information on the primary yields of various dissociation channels plays a crucial role in constructing a reliable photochemical model for earth and planetary atmospheres, in particular that of Titan, which is the largest moon of Saturn and its atmosphere is composed of about 2% of methane and 98% of N 2 . , In addition, the dissociated CH, CH 2 , and CH 3 radicals can undergo subsequent collisions, thereby providing the synthetic route to the higher hydrocarbons and other organic molecules observed in the atmosphere of the outer planets such as Jupiter, Saturn, and their satellites. , .25ex2ex lefttrue C H 4 false( X̃ A 1 1 false) + h v false( 118 .25em n m false) → C H 3 false( X̃ A 2 ″ 2 false) + H Δ H = 6.01 normale normalV false( 1 normala false) <...…”

Fragmentation of Molecules by Virtual Photons from Remote Neighbors

“…Our examples are the nitrogen (N 2 ), water (H 2 O), and methane (CH 4 ) molecules which, being common molecules of interest, have been much studied. See refs and − and references therein. As neighbors, we choose rare gas atoms, which are of interest by themselves and often serve in experiments as matrices to trap and investigate molecules, and importantly, the required data to evaluate (eq ) is available for them.…”