Infrared Action Spectroscopy and Inelastic Recoil Dynamics of the CH<sub>4</sub>−OD Reactant Complex

Tsiouris, Maria; Pollack, I. B.; Lester, Marsha I.

doi:10.1021/jp0209143

Cited by 5 publications

(14 citation statements)

References 36 publications

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“…1,2,4,10,15 In these experiments, OD radicals were generated by the 193 nm photolysis of commercially custom-synthesized DNO 3 ͑90 wt. %, Isotech͒ in a 10% CO, balance Ne carrier gas mixture ͑225 psi͒ using an ArF excimer laser ͑Lambda Physik Compex 102͒.…”

Section: Experimental Methodsmentioning

confidence: 99%

Infrared action spectroscopy and time-resolved dynamics of the OD–CO reactant complex

Pollack

Tsiouris

Leung

et al. 2003

The Journal of Chemical Physics

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The infrared action spectrum of the linear OD–CO reactant complex has been recorded in the OD overtone region near 1.9 μm using an infrared pump-ultraviolet probe technique. The pure overtone band of OD–CO (2νOD) is observed at 5148.6 cm−1 and combination bands involving the simultaneous excitation of OD stretch and D-atom bend are identified 160.0 and 191.2 cm−1 to higher energy. Band assignments and spectroscopic constants are derived from the rotationally resolved structure of the spectra. The change in the ground state rotational constant upon deuteration demonstrates that the H/D-atom of the hydroxyl radical points toward CO in the OH/D-CO complex. Direct time-domain measurements yield a lifetime of 37(4) ns for OD–CO (2νOD) prior to decay via inelastic scattering or chemical reaction. This is significantly longer than the laser-limited lifetime of ⩽5 ns observed for OH–CO (2νOH), and is attributed in part to the closing of a near-resonant vibration to vibration energy transfer channel upon deuteration. Vibrational predissociation of OD–CO (2νOD) proceeds by a vibration to rotation and/or translation mechanism that yields highly rotationally excited OD (v=1) fragments. Intermolecular D-atom bend excitation, which drives the structural transformation from the reactant complex to the transition state for reaction, results in a dramatic shortening of the lifetime to ⩽6 ns (laser-limited). Excitation of the D-atom bend also supplies sufficient energy to reopen the near-resonant vibrational energy transfer channel, resulting in minimal rotational excitation of the OD (v=1) fragments. Finally, a ground state binding energy for OD–CO of D0⩽456 cm−1 is established from the OD (v=1) product state distribution.

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Section: Experimental Methodsmentioning

confidence: 99%

Infrared action spectroscopy and time-resolved dynamics of the OD–CO reactant complex

Pollack

Tsiouris

Leung

et al. 2003

The Journal of Chemical Physics

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“…In comparison, the OD stretch can decay to one quanta of CH 4 bend, requiring the redistribution of twice the excess energy as for OH (∼1100 cm –1 ). This suggests that the narrower (broader) lines in the OD (OH) stretching fundamentals result from a larger (smaller) energy gap between the excited state and nearest accessible relaxation channel; i.e., the difference in lifetimes is due to faster V–V transfer in OH–CH 4 , which is similar to what was observed in the gas phase overtone spectra. , …”

Section: Resultsmentioning

confidence: 52%

“…The faster decay of the excited state for OH–CH 4 was broadly attributed to prereaction and/or predissociation. Analysis of the rotational energy distribution of the predissociated OX radicals more specifically indicated that near resonant V–V transfer is responsible for the faster decay in OH–CH 4 compared to OD–CH 4 . In helium nanodroplets we see a similar reduction in the linewidths in going from OH [0.035(5) cm –1 ] to OD [0.013(3) cm –1 ].…”

Section: Resultsmentioning

confidence: 76%

“… a Ground state constant from ref . b Ground state constant from ref . c Difference between B ′ and B ″ fixed to value for OD–CH 4 . d Fixed to value for OD–CH 4 . e Fixed to value for OH–CD 4 . f Assumed scaled value g Central unresolved Q branch peak. h Full-width at half-maximum linewidth. …”

Section: Resultsmentioning

confidence: 99%

“…Its OD stretching overtone spectrum was reported, which can be directly compared to the OH stretching overtone spectrum for the normal isotopologue . The comparison shows that there is a large reduction in the linewidth in the gas phase in going from OH [0.21(2) cm –1 ] to OD [0.10(1) cm –1 ] . The faster decay of the excited state for OH–CH 4 was broadly attributed to prereaction and/or predissociation.…”

Section: Resultsmentioning

confidence: 99%

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Infrared Spectroscopy of the Entrance Channel Complex Formed Between the Hydroxyl Radical and Methane in Helium Nanodroplets

Obi

Douberly

2017

J. Phys. Chem. A

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The entrance channel complex in the exothermic OH + CH → HO + CH reaction has been isolated in helium nanodroplets following the sequential pick-up of the hydroxyl radical and methane. The a-type OH stretching band was probed with infrared depletion spectroscopy, revealing a spectrum qualitatively similar to that previously reported in the gas phase, but with additional substructure that is due to the different internal rotation states of methane (j = 0, 1, or 2) in the complex. We fit the spectra by assuming the rotational constants of the complex are the same for all internal rotation states; however, subband origins are found to decrease with increasing j. Measurements of deuterated complexes have also been made (OD-CH, OH-CD, and OD-CD), the relative linewidths of which provide information about the flow of vibrational energy in the complexes; vibrational lifetime broadening is prominent for OH-CH and OD-CD, for which the excited OX stretching state has a nearby CY stretching fundamental (X, Y = H or D).

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Infrared Activated Signatures and Jahn–Teller Dynamics of NO–CH₄Collision Complexes

Davis,

Neisser,

Kidwell

2023

J. Phys. Chem. A

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Bimolecular collision outcomes sensitively depend on the chemical functionality and relative orientations of the colliding partners that define the accessible reactive and nonreactive pathways. Accurate predictions from multidimensional potential energy surfaces demand a full characterization of the available mechanisms. Therefore, there is a need for experimental benchmarks to control and characterize the collision conditions with spectroscopic accuracy to accelerate the predictive modeling of chemical reactivity. To this end, the bimolecular collision outcomes can be investigated systematically by preparing reactants in the entrance channel prior to reaction. Herein, we investigate the vibrational spectroscopy and infrared-driven dynamics of the bimolecular collision complex between nitric oxide and methane (NO–CH4). We recorded the vibrational spectroscopy of NO–CH4 in the CH4 asymmetric stretching region using resonant ion-depletion infrared spectroscopy and infrared action spectroscopy, thus revealing a significantly broad spectrum centered at 3030 cm–1 that extends over 50 cm–1. The asymmetric CH stretch feature of NO–CH4 is explained by CH4 internal rotation and attributed to transitions involving three different nuclear spin isomers of CH4. The vibrational spectra also show extensive homogeneous broadening due to the ultrafast vibrational predissociation of NO–CH4. Additionally, we combine infrared activation of NO–CH4 with velocity map imaging of NO (X 2Π, ν″ = 0, J″, F n, Λ) products to develop a molecular-level understanding of the nonreactive collisions of NO with CH4. The anisotropy of the ion image features is largely determined by the probed rotational quantum number of NO (J″) products. For a subset of NO fragments, the ion images and total kinetic energy release (TKER) distributions show an anisotropic component at low relative translation (∼225 cm–1) indicating a prompt dissociation mechanism. However, for other detected NO products, the ion images and TKER distributions are bimodal, in which the anisotropic component is accompanied by an isotropic feature at high relative translation (∼1400 cm–1) signifying a slow dissociation pathway. In addition to the predissociation dynamics following vibrational excitation, the Jahn–Teller dynamics prior to infrared activation need to be considered to fully describe the product spin–orbit distributions. Therefore, we correlate the Jahn–Teller mechanisms of NO–CH4 to the symmetry-restricted NO (X 2Π, ν″ = 0, J″, F n, Λ) + CH4 (ν″) product outcomes.

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Infrared Action Spectroscopy and Inelastic Recoil Dynamics of the CH₄−OD Reactant Complex

Cited by 5 publications

References 36 publications

Infrared action spectroscopy and time-resolved dynamics of the OD–CO reactant complex

Infrared action spectroscopy and time-resolved dynamics of the OD–CO reactant complex

Infrared Spectroscopy of the Entrance Channel Complex Formed Between the Hydroxyl Radical and Methane in Helium Nanodroplets

Infrared Activated Signatures and Jahn–Teller Dynamics of NO–CH₄Collision Complexes

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Infrared Action Spectroscopy and Inelastic Recoil Dynamics of the CH4−OD Reactant Complex

Cited by 5 publications

References 36 publications

Infrared action spectroscopy and time-resolved dynamics of the OD–CO reactant complex

Infrared action spectroscopy and time-resolved dynamics of the OD–CO reactant complex

Infrared Spectroscopy of the Entrance Channel Complex Formed Between the Hydroxyl Radical and Methane in Helium Nanodroplets

Infrared Activated Signatures and Jahn–Teller Dynamics of NO–CH4Collision Complexes

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Product

Resources

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Infrared Action Spectroscopy and Inelastic Recoil Dynamics of the CH₄−OD Reactant Complex

Infrared Activated Signatures and Jahn–Teller Dynamics of NO–CH₄Collision Complexes