Photodissociation: a critical survey

128

Rovibronic state to rovibronic state reaction dynamics: O(3 P)+HCl(v=2,J)→OH(v′,N′)+Cl(2 P) Complete rotational distributions have been obtained for the CO produced following excitation of H 2 CO, HDCO, and D 2 CO near the S 1 origin. The CO was detected by vacuum ultraviolet laser-induced fluorescence. The distributions show a remarkable amount of rotational excitation, peaking at J = 42, 49, and 53 for H 2 CO, HDCO, and D 2 CO, respectively, with widths of 20-25 J units (FWHM). CO(v = 1) from H 2 CO photolysis has nearly the same rotational distribution as CO(v = 0). The population of CO(v = 1) is 14%±5% as large as the population of CO (v = 0), in good agreement with earlier measurements. Increased angular momentum of H CO is only partially transferred to CO, giving slightly wider rotational distributi~ns without changing the peak value. The rotational distributions are highly nonthermal, showing that energy randomization does not occur during the dissociation event. An approximate range of product impact parameters has been determined. The impact parameters are too large to be accounted for by forces along the directions of the C-H bonds. The hydrogen ~ppears to be most strongly repelled by the charge distribution a fraction of an A outside the carbon atom of the CO. The distribution of impact parameters and the internal energy of the hydrogen fragment apparently do not change significantly upon isotopic substitution. The absence of population in CO(J < 20) confirms the identity of CO(J > 25) as the long-lived intermediate in formaldehyde photodissociation.3032

Section: B Photodissociation Dynamicsmentioning

confidence: 99%

Photofragmentation dynamics of formaldehyde: CO(v,J) distributions as a function of initial rovibronic state and isotopic substitution

Bamford

Filseth

Foltz

et al. 1985

128

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] The laser-induced fluorescence ͑LIF͒ has been widely used to probe the alignment and orientation of molecular angular momentum. [21][22][23][24][25] Several typical theoretical approaches have been used to extract alignment or orientation parameters from measured LIF intensity or two-photon absorption spectroscopy.…”

Section: Introductionmentioning

confidence: 99%

Theory for determining alignment parameters of symmetric top molecule using (n+1) LIF

Cong

Han

Lou

2000

Expressions used for extracting the population and alignment parameters of a symmetric top molecule from (nϩ1) laser-induced fluorescence ͑LIF͒ are derived by employing the tensor density matrix method. The molecular population and alignment are described by molecular state multipoles. The LIF intensity is a complex function of the initial molecular state multipoles, the dynamic factors, and the excitation-detection geometrical factors. The problem of how to extract the initial molecular state multipoles from (2ϩ1)LIF, as an example, is discussed in detail.

“…The photodissociation of triatomic molecules has long been recognized as a prototypical dynamical process that is amenable to both detailed experimental study [1][2][3][4][5] and theoretical calculations. [6][7][8][9][10][11][12][13] Although full quantum descriptions are possible for some triatomic dissociations, approximate theoretical treatments and models of photofragmentation dynamics provide invaluable insights into the interpretation of experimental photoabsorption spectra.…”

Section: Introductionmentioning

confidence: 99%

Three-dimensional infinite order sudden quantum theory for indirect photodissociation processes. Application to the photofragment yield spectrum of NOCl in the region of the T1(13A″) ←S(11A′) transition. Fragment rotational distributions and thermal averages

Grinberg

Freed

Williams

1997

The analytical infinite order sudden ͑IOS͒ quantum theory of triatomic photodissociation, developed in paper I, is applied to study the indirect photodissociation of NOCl through a real or virtual intermediate state. The theory uses the IOS approximation for the dynamics in the final dissociative channels and an Airy function approximation for the continuum functions. The transition is taken as polarized in the plane of the molecule; symmetric top wave functions are used for both the initial and intermediate bound states; and simple semiempirical model potentials are employed for each state. The theory provides analytical expressions for the photofragment yield spectrum for producing particular final fragment ro-vibrational states as a function of the photon excitation energy. Computations are made of the photofragment excitation spectrum of NOCl in the region of the T 1 (1 3 AЉ) ←S 0 (1 1 AЈ) transition for producing the NO fragment in the vibrational states n NO ϭ0, 1, and 2. The computed spectra for the unexcited n NO ϭ ϭ0 and excited n NO ϭ2 states are in reasonable agreement with experiment. However, some discrepancies are observed for the singly excited n NO ϭ1 vibrational state, indicating deficiencies in the semiempirical potential energy surface. Computations for two different orientations of the in-plane transition dipole moment produce very similar excitation spectra. Calculations of fragment rotational distributions are performed for high values of the total angular momentum J, a feature that would be very difficult to perform with close-coupled methods. Computations are also made of the thermally averaged rotational energy distributions to simulate the conditions in actual supersonic jet experiments.