Methyl rotation, vibration, and alignment from a multiphoton ionization study of the 266 nm photodissociation of methyl iodide

Loo, Rachel Ogorzalek; Haerri, Hans-Peter; Hall, Gregory E.; Houston, Paul L.

doi:10.1063/1.455779

Cited by 201 publications

(33 citation statements)

References 66 publications

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“…63 The analyses gave a population ratio of CH 3 (ν ) 0): CH 3 (ν 2 ) 1) ) 1:0.47 for all methyl products. This ratio is consistent with the ratio of 1:0.41 reported by Trentelman et al using nanosecond (ns) laser REMPI detection.…”

Section: Competition Between Ivr and Dissociationmentioning

confidence: 99%

Ultrafast Photodissociation Dynamics of Acetone at 195 nm: I. Initial-state, Intermediate, and Product Temporal Evolutions by Femtosecond Mass-Selected Multiphoton Ionization Spectroscopy

Chen

Cheng

2005

J. Phys. Chem. A

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The photodissociation dynamics of the acetone S2 (n, 3s) Rydberg state excited at 195 nm has been studied by using femtosecond pump-probe mass-selected multiphoton ionization spectroscopy. For the first time, the temporal evolutions of the initial state, intermediates, and methyl products were simultaneously measured and analyzed for this reaction to elucidate the complex dynamics. Two mechanisms were considered: (1) the commonly accepted mechanism in which the primary dissociation occurs on the first triplet-state surface, and (2) the recently proposed mechanism in which the primary dissociation takes place on the first singlet-excited-state surface. Our results and analyses supported the validity of the new mechanism. On the other hand, the conventional mechanism was found to be inadequate to describe the observed dynamics. The temporal evolution of methyl products arising from the secondary dissociation of hot acetyl intermediates exhibited a very complex behavior that can be ascribed to the combination of a nonuniform initial vibrational distribution and the competition between dissociation and slow intramolecular vibrational redistribution.

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Section: Competition Between Ivr and Dissociationmentioning

confidence: 99%

Ultrafast Photodissociation Dynamics of Acetone at 195 nm: I. Initial-state, Intermediate, and Product Temporal Evolutions by Femtosecond Mass-Selected Multiphoton Ionization Spectroscopy

Chen

Cheng

2005

J. Phys. Chem. A

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“…It would also be very intriguing to further elucidate the mechanism and sources of the absorption intensity enhancement and redshifts of the A and B bands of bromoiodomethane relative to the single chromophore iodomethane and bromomethane molecules. Many of the experimental techniques such as molecular beam experiments, [101][102][103][104][105]107 magnetic circular dichroism ͑MCD͒, 85 multiphoton ionization ͑MPI͒, 107,[126][127][128] infrared emission, 106 coherent anti-Stokes Raman scattering ͑CARS͒, 129 diode laser absorption, 130 femtosecond time-resolved pump-probe experiments, 95 and others that have proved so useful to study iodomethane A-band photodissociation are readily applicable to the bromoiodomethane system. The bromoiodomethane molecular system appears ripe for a wide variety of experimental and possibly theoretical work by many different research groups to help create a much more detailed under-standing of its bond selective electronic excitation and photochemistry.…”

Section: Coupling Of the C-i And C-br Chromophores And Future Prosmentioning

confidence: 99%

Short-time photodissociation dynamics of A-band and B-band bromoiodomethane in solution: An examination of bond selective electronic excitation

Shi-Qing

Kwok

Phillips

et al. 1996

The Journal of Chemical Physics

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We have obtained resonance Raman spectra and absolute Raman cross section measurements at eight excitation wavelengths in the A-band and B-band absorptions of bromoiodomethane in cyclohexane solution. The resonance Raman intensities and absorption spectra were simulated using a simple model and time-dependent wave packet calculations. Normal mode vibrational descriptions were used with the results of the calculations to find the short-time photodissociation dynamics in terms of internal coordinates. The A-band short-time photodissociation dynamics indicate that the C-I bond becomes much longer, the C-Br bond becomes smaller, the I-C-Br angle becomes smaller, the H-C-Br angles become larger, the H-C-I angles become smaller, and the H-C-H angle becomes a bit smaller. The B-band short-time photodissociation dynamics indicate the C-Br bond becomes much longer, the C-I bond becomes slightly longer, the I-C-Br angle becomes smaller, the H-C-I angles become larger, the H-C-Br angles become smaller, and the H-C-H angle becomes slightly smaller. Both the A-band and B-band short-time photodissociation dynamics appear to be most consistent with an impulsive ''semi-rigid'' radical model qualitative description of the photodissociation with the CH 2 Br radical changing to a more planar structure in the A-band and the CH 2 I radical changing to a more planar structure in the B band. We have carried out a Gaussian deconvolution of the A-band and B-band absorption spectra of bromoiodomethane, as well as iodomethane and bromomethane. The absorption spectra, resonance Raman intensities, and short-time photodissociation dynamics suggest a moderate amount of coupling of the C-I and C-Br chromophores.

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“…Other experiments on the A-band photodissociation of iodomethane have investigated the translational energy of the photofragments, 44,45 the vibrational excitation of the methyl fragment, 44,[46][47][48][49][50] and the I/I* branching ratio. [51][52][53] Unlike most alkyl halide A-band photodissociation reactions, iodomethane has had a number of vibrational mode-specific techniques applied to examine its photodissociation.…”

Section: Introductionmentioning

confidence: 99%

Early-time photodissociation dynamics of chloroiodomethane in the A-band absorption from resonance Raman intensity analysis

Kwok

Phillips

1996

The Journal of Chemical Physics

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We have obtained resonance Raman spectra and absolute Raman cross sections for h 2-chloroiodomethane ͑fourteen excitation wavelengths between 200 nm and 355 nm͒ and d 2-chloroiodomethane ͑for 282.4 nm excitation͒ in cyclohexane solution. Most of the intensity in the A-band resonance Raman spectra appears in the nominal C-I stretch overtones progression and combination bands of the nominal C-I stretch overtones with the fundamentals of the CH 2 wag, CH 2 scissor, and the Cl-C-I bend or C-Cl stretch fundamentals. The A-band absorption and absolute resonance Raman intensities were simulated using a simple model which included preresonant contributions to the fundamental Raman peaks and time-dependent wave packet calculations. The motion of the wave packet on the excited state surface was converted from dimensionless normal coordinates into internal coordinates using the results of normal coordinate calculations. The A-band short-time photodissociation dynamics of chloroiodomethane shows that the C-I bond lengthens, the I-C-Cl and H-C-I angles become smaller, and the H-C-Cl angles become larger. These internal coordinate motions which are associated with relatively low frequency modes are consistent with a simple impulsive ''soft'' radical model of the photodissociation and the CH 2 Cl group changing to a more planar structure. However, the C-H bond length does not change much and the H-C-H angle ͑associated with higher frequency modes͒ becomes slightly smaller which is inconsistent with the ''soft'' radical model and the CH 2 Cl group changing to a more planar structure. This suggests that an impulsive ''semirigid'' radical model may be more appropriate than the ''soft'' radical model to qualitatively describe the chloroiodomethane photodissociation. An ambiguity in the assignment of the 724 cm Ϫ1 Raman peak and its associated combination bands to combination bands of the nominal C-I stretch overtones with the fundamentals of the Cl-C-I bend or C-Cl stretch fundamentals limits what we are able to determine about the C-Cl bond length changes during the initial stages of the photodissociation.

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Methyl rotation, vibration, and alignment from a multiphoton ionization study of the 266 nm photodissociation of methyl iodide

Cited by 201 publications

References 66 publications

Ultrafast Photodissociation Dynamics of Acetone at 195 nm: I. Initial-state, Intermediate, and Product Temporal Evolutions by Femtosecond Mass-Selected Multiphoton Ionization Spectroscopy

Ultrafast Photodissociation Dynamics of Acetone at 195 nm: I. Initial-state, Intermediate, and Product Temporal Evolutions by Femtosecond Mass-Selected Multiphoton Ionization Spectroscopy

Short-time photodissociation dynamics of A-band and B-band bromoiodomethane in solution: An examination of bond selective electronic excitation

Early-time photodissociation dynamics of chloroiodomethane in the A-band absorption from resonance Raman intensity analysis

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