A 1 + 1′ resonance-enhanced multiphoton ionization scheme for rotationally state-selective detection of formaldehyde via the à ¹A₂ ← X̃ ¹A₁ transition

Abstract

The formaldehyde molecule is an important model system for understanding dynamical processes in small polyatomic molecules. However, prior to this work, there have been no reports of a resonance-enhanced multiphoton ionization (REMPI) detection scheme for formaldehyde suitable for rovibrationally state-selective detection in molecular beam scattering experiments. Previously reported tunable REMPI schemes are either non-rotationally resolved, involve multiple resonant steps, or involve many-photon ionization steps. In the current work, we present a new 1 + 1' REMPI scheme for formaldehyde. The first photon is tunable and provides rotational resolution via the vibronically allowed à (1)A2 ← X[combining tilde] (1)A1 transition. Molecules are then directly ionized from the à state by one photon of 157 nm. The results indicate that the ionization cross section from the 4(1) vibrational level of the à state is independent of the rotational level used as intermediate, to within experimental uncertainty. The 1 + 1' REMPI intensities are therefore directly proportional to the à ← X[combining tilde] absorption intensities and can be used for quantitative measurement of X[combining tilde]-state population distributions.

Intermediate state dependence of the photoelectron circular dichroism of fenchone observed via femtosecond resonance-enhanced multi-photon ionization

“…The TOF spectrometer used in the experiment has been described earlier. 43 Briefly, fenchone is evaporated by resistive heating of a reservoir coupled to a pulsed nozzle synchronized to the laser. The vapor is expanded using a backing pressure of 6 bar H 2 .…”

Vibrational Energy Redistribution in a Gas-Surface Encounter: State-to-State Scattering of CH4 from Ni(111)

“…Because of the wide dispersion of scattering products in space, time, and internal state, experimentalists have so far relied mostly on the very sensitive resonantly enhanced multiphoton ionization (REMPI) method for state-resolved detection. However, the systems accessible with REMPI or LIF are with few exceptions [12][13][14][15] limited to atoms and diatomic molecules. Consequently, previous surface scattering studies have mainly focused on these species.…”

“…By contrast, studies that probe the postscattering state distributions of polyatomic molecules remain scarce [12][13][14][15][16][17][18][19][20]. This is unfortunate since the dynamics of polyatomics at surfaces are expected to be rich and distinctly different from those of diatomics, not least due to the additional vibrational degrees of freedom (d.o.f.)…”

Photodissociation Dynamics of CO-Forming Channels on the Ground-State Surface of Methyl Formate at 248 nm: Direct Dynamics Study and Assessment of Generalized Multicenter Impulsive Models

“…Velocity imaging on H 2 , obtained by ionization of H 2 , might help shed light on the existence of TS2. Laser-induced fluorescence or multiphoton ionization of the H 2 CO product, after 248 nm photolysis of methyl formate, may also give important information on the mechanism. Recall that when comparing with the present TS2 data (Figure ), the translational energy of CO peaks at around 5–10 kcal/mol, which is compatible with the fast component in the previous velocity map imaging study at 248 nm …”