Frequency modulated circular dichroism spectroscopy: application to ICN photolysis

Hancock, Gus; Richmond, Graham; Ritchie, Grant A. D.; Taylor, Sarah; Costen, Matthew L.; Hall, Gregory E.

doi:10.1080/00268971003649323

Cited by 6 publications

(18 citation statements)

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“…Now we discuss about the experimental results by Hall et al Their molecular frame orientations for each of the F 1 and F 2 levels, given in their Figures and of Ref. , show an almost similar behavior.…”

Section: Discussionmentioning

confidence: 59%

“…Furthermore, since the N dependence of the photofragment CN( v = 0) orientation correlated well with the behavior of the I*/I branching ratio, and the net orientation was zero for the photofragments CN( v = 2), which were observed only with the I( 2 P 3/2 ) dissociation partners, spin–orbit interaction was believe to be essential for the orientation of photofragment CN . Following the earlier work, Hall et al studied the bipolar moment of CN products by the frequency modulation spectroscopy . They reported the orientation parameters for each of the F 1 and F 2 levels for the coincident atomic I and I* states, and found no notable difference between the F 1 / F 2 levels in both I and I* channels.…”

Section: Introductionmentioning

confidence: 85%

“…The product CN has the electronic ground state of X 2 Σ + , thus each rotational level N is split in the fine structure levels F 1 ( J = N + 1/2) and F 2 ( J = N − 1/2) due to the spin–rotation interaction (SRI). In the past photodissociation experiments, the F 1 / F 2 level distributions for each N were found to be non‐statistical, and the population difference function f ( N ) defined by Zare et al with their populations P ( F 1 ) and P ( F 2 )

f ((), N) = \frac{P ((), F_{1}) - P ((), F_{2})}{P ((), F_{1}) + P ((), F_{2})}

depended systematically on the excitation wavelength λ and the rotation level N . This interesting result has been known for over 30 years, but the detailed mechanism remains unsolved.…”

Section: Introductionmentioning

confidence: 95%

“…The

\overset{A}{true}

‐band ( λ = 210–320 nm) photodissociation of ICN in the gas phase, especially its fragment branching ratios and the stereo dynamics, have suggested the presence of complicated nonadiabatic transitions, and prompted many experimental and theoretical studies over the past 30 years, as described in many reviews and monographs . The following two dissociation channels are known experimentally.

ICN + hν \to \frac{0pt}{normalI ((), {}^{2}{P_{3 / 2}}) + CN ((), X {{}^{2}Σ}^{+} v, N, F_{1} / F_{2})} .

…”

Section: Introductionmentioning

confidence: 99%

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Potential energy surfaces and nonadiabatic transitions in the asymptotic regions of ICN photodissociation to study the interference effects in the F₁ and F₂ spin‐rotation levels of the CN products

et al. 2018

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One of the most spectacular yet unsolved problems for the ICÑ A-band photodissociation is the non-statistical spin-rotation F 1 = N + 1/2 and F 2 = N − 1/2 populations for each rotation level N of the CN fragment. The F 1 /F 2 population difference function f(N) exhibits strong N and λ dependences with an oscillatory behavior. Such details were found to critically depend on the number of open-channel product states, namely, whether both I ( 2 P 3/2 ) and I ( 2 P 1/2 ) are energetically available or not as the dissociation partner. First, in the asymptotic region, the exchange and dipole-quadrupole inter-fragment interactions were studied in detail. Then, as the diabatic basis, we took the appropriate symmetry adapted products of the electronic and rotational wavefunctions for the F 1 and F 2 levels at the dissociation limits. We found that the adiabatic Hamiltonian exhibits Rosen-Zener-Demkov type nonadiabatic transitions reflecting the switch between the exchange interaction and the small but finite spin-rotation interaction within CN at the asymptotic region. This non-crossing type nonadiabatic transition occurs with the probability 1/2, that is, at the diabatic limit through a sudden switch of the quantization axis for CN spin S from the dissociation axis to the CN rotation axis N. We have derived semiclassical formulae for f(N) and the orientation parameters with a two-state model including the 3A 0 and 4A 0 electronic states, and with a four-state model including the 3A 0 through 6A 0 electronic states. These two kinds of interfering models explain general features of the F 1 and F 2 level populations observed by Zare's group and Hall's group, respectively.It is known that the ground state of the I atom has j = 3/2, thus yields the non-zero quadrupole moment due to the non-spherical charge distribution, while the spin-orbit excited state has j = 1/2, WWW.C-CHEM.ORG FULL PAPERWiley Online Library J. Comput. Chem. 2019, 40, 482-499 485 the space-fixed (SF) Z 0 axis is taken as the propagation direction for circularly polarized light (Fig. 2). Then, we focus on the orientation of the SF total angular momentum of photofragment CN. This orientation is defined asHere, J Z 0 M SF J is the space-fixed Z 0 component of the total angular momentum CN, and ρ J ð Þ M SF J M SF J is the relative population observed in the level M SF J and is normalized as P M SF J ρ J ð Þ M SF J M SF J

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Section: Discussionmentioning

confidence: 59%

Section: Introductionmentioning

confidence: 85%

f ((), N) = \frac{P ((), F_{1}) - P ((), F_{2})}{P ((), F_{1}) + P ((), F_{2})}

depended systematically on the excitation wavelength λ and the rotation level N . This interesting result has been known for over 30 years, but the detailed mechanism remains unsolved.…”

Section: Introductionmentioning

confidence: 95%

“…The

\overset{A}{true}

ICN + hν \to \frac{0pt}{normalI ((), {}^{2}{P_{3 / 2}}) + CN ((), X {{}^{2}Σ}^{+} v, N, F_{1} / F_{2})} .

…”

Section: Introductionmentioning

confidence: 99%

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Potential energy surfaces and nonadiabatic transitions in the asymptotic regions of ICN photodissociation to study the interference effects in the F₁ and F₂ spin‐rotation levels of the CN products

et al. 2018

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“…39,41,[79][80][81][82] We note that the Re[Ā k 1 ] parameter is proportional to two terms, an in-plane component (proportional to cosϕ A ), and an out-of-plane component (proportional to sinϕ A ). (12)-(13) can be nonzero for photodissociation via a single dissociative state, due to the breakdown of the URD approximation (otherwise, within the URD approximation, for χ A = 0 and ϕ A = 0, these parameters reduce to zero as is clear from inspection, and as is described in Sec.…”

Section: B Breakdown Of Urd Approximation For Single-state Photodissmentioning

confidence: 99%

Photofragment angular momentum distributions in the molecular frame. III. Coherent effects in the photodissociation of polyatomic molecules with circularly polarized light

Rakitzis

2010

The Journal of Chemical Physics

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We extend the a(q) (k)(s) polarization parameter model [T. P. Rakitzis and A. J. Alexander, J. Chem. Phys. 132, 224310 (2010)] to describe the components of the product angular momentum polarization that arise from the one-photon photodissociation of asymmetric top molecules with circularly polarized photolysis light, and provide a general equation for fitting experimental signals. We show that the only polarization parameters that depend on the helicity of the circularly polarized photolysis light are the A(0) (k) and Re[A(1) (k)] (with odd k) and the Im[A(1) (k)] (with even k); in addition, for the unique recoil destination (URD) approximation [for which the photofragment recoil v arises from a unique parent molecule geometry], we show that these parameters arise only as a result the interference between at least two dissociative electronic states. Furthermore, we show that in the breakdown of the URD approximation (for which the photofragment recoil v arises from a distribution of parent molecule geometries), these parameters can also arise for dissociation via a single dissociative electronic state. In both cases, the A(0) (k) and Re[A(1) (k)] parameters (with odd k) are proportional to cosΔφ, and the Im[A(1) (k)] parameters (with even k) are proportional to sinΔφ, where Δφ is the phase shift (or average phase shift) between the interfering paths so that Δφ can be determined directly from the A(q) (k), or from ratios of these A(q) (k) parameters. Therefore, the determination of these A(q) (k) parameters with circularly polarized photolysis light allows the unambiguous measurement of coherent effects in polyatomic-molecule photodissociation.

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Dynamic Mapping of CN Rotation Following Photoexcitation of ICN⁻

et al. 2012

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The ICN molecule is a prototype for the study of dynamics at conical intersections; [1] 266 nm photoexcitation to the A continuum [2] produces a bimodal distribution of CN photofragment rotations identified with different I-atom partner fragments [Equations (1) and (2)]:Trajectory calculations that were run on high-level potential energy surfaces [4] established that bending motion, which occurs along with the IÀCN bond elongation, maps into torque on the CN as ICN passes through a conical intersection, giving the notably high degree of rotational excitation observed in concurrence with I( 2 P 3/2 ). Condensed-phase ICN photodissociation studies also observe this significant degree of rotation, [5] and even in the strongly interacting solvent water, the CN fragment is initially born as a free rotor. [6] In the absence of a conical intersection, the shape of the excited-state potential energy surface still plays a large role in the rotational-state distribution of the photofragments. An isotropic excited-state surface simply converts any original bending motion into rotation of the fragments upon bond cleavage, resulting in a small degree of rotational excitation. However, the presence of anisotropy on the excited-state surface induces torque that initiates additional rotational motion in the fragments and can lead to a much larger degree of rotational excitation. These exit channel dynamics convey the efficiency of translational to rotational energy transfer. The photodissociation of H 2 O 2 serves as an instructive example, in which the OH rotational-state distribution reflects both the torsional wavefunction of the electronic ground state and the anisotropy of the excited-state surfaces. [7] In a confined environment, the relaxation of rotational excitation will influence the subsequent dynamics. Molecular dynamics simulations of ICN photodissociation in solid and liquid Ar were performed on the two excited-state potential energy surfaces ( 3 P 0+ and 1 P 1 ) that form the conical intersection. [8] These simulations found complete cage recombination in the solid, along with differences in the cageinduced isomerization dynamics; both ICN and INC form on the 3 P 0+ surface, while only ICN is found on the 1 P 1 surface. In this model, which neglects nonadiabatic transitions, the contrasting anisotropies of the ICN excited-state potential energy surfaces give rise to different rotational-relaxation dynamics. These relaxation dynamics, along with the CNrotation barriers, are responsible for the dissimilar isomerization yields.Herein we investigate the excited-state dynamics of ICN À (Ar) n for n = 0-5 using excitation energies between 2.5 and 4.2 eV. Specifically, we focus on the role of CN fragment rotation in the dynamics of photoexcited ICN À with and without Ar solvation. Figure 1 sketches potential energy curves adapted from Ref. [9] for the electronic ground state of the ICN À and INC À isomers ( 2 S + , red) and the first optically accessible excited state of these isomers ( 2 P 1/2 , blue), along Figure 1...

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Frequency modulated circular dichroism spectroscopy: application to ICN photolysis

Cited by 6 publications

References 50 publications

Potential energy surfaces and nonadiabatic transitions in the asymptotic regions of ICN photodissociation to study the interference effects in the F₁ and F₂ spin‐rotation levels of the CN products

Potential energy surfaces and nonadiabatic transitions in the asymptotic regions of ICN photodissociation to study the interference effects in the F₁ and F₂ spin‐rotation levels of the CN products

Photofragment angular momentum distributions in the molecular frame. III. Coherent effects in the photodissociation of polyatomic molecules with circularly polarized light

Dynamic Mapping of CN Rotation Following Photoexcitation of ICN⁻

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Frequency modulated circular dichroism spectroscopy: application to ICN photolysis

Cited by 6 publications

References 50 publications

Potential energy surfaces and nonadiabatic transitions in the asymptotic regions of ICN photodissociation to study the interference effects in the F1 and F2 spin‐rotation levels of the CN products

Potential energy surfaces and nonadiabatic transitions in the asymptotic regions of ICN photodissociation to study the interference effects in the F1 and F2 spin‐rotation levels of the CN products

Photofragment angular momentum distributions in the molecular frame. III. Coherent effects in the photodissociation of polyatomic molecules with circularly polarized light

Dynamic Mapping of CN Rotation Following Photoexcitation of ICN−

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Potential energy surfaces and nonadiabatic transitions in the asymptotic regions of ICN photodissociation to study the interference effects in the F₁ and F₂ spin‐rotation levels of the CN products

Potential energy surfaces and nonadiabatic transitions in the asymptotic regions of ICN photodissociation to study the interference effects in the F₁ and F₂ spin‐rotation levels of the CN products

Dynamic Mapping of CN Rotation Following Photoexcitation of ICN⁻