The multiconfigurational time‐dependent Hartree (MCTDH) approximation to the time‐dependent Schrodinger equation is tested for a realistic three‐dimensional example, the photodissociation of NOCl. The working equations of the MCTDH scheme introduced earlier are discussed in some detail. A computational scheme is presented which allows for efficient numerical MCTDH calculations. This scheme is applied to the photodissociation of NOCl after excitation to the S1 surface. The results are compared to the results of an exact wave‐packet dynamics calculation. Fast convergence of the MCTDH results toward the exact one is found as the number of configurations is increased. The computation times of the MCTDH calculations are found to be much shorter than those of the exact calculation. Even MCTDH calculations including sufficiently many configurations for a fully converged (quasiexact) description require over two orders of magnitude less CPU time than an exact calculation. The so‐called ‘‘natural populations’’ tha...

Wave‐packet dynamics within the multiconfiguration Hartree framework: General aspects and application to NOCl

Velocity‐aligned, superthermal O(1D) atoms generated via the photodissociation of N2O have been employed to investigate the stereodynamics of the title reaction. The power of this experimental technique, when coupled with Doppler‐resolved, polarized laser‐induced fluorescence probing of the reaction products, is demonstrated by reference to the specific reaction channel leading to NO(υ’=0)+NO(υ’=16,17), which is shown to proceed via direct stripping dynamics. Furthermore, the observed product‐state selective linear and angular momenta disposals imply that the reaction is stereodynamically constrained to occur via collinear collision geometries.

The stereochemistry of the O(1D)+N2O→NO+NO reaction via velocity‐aligned photofragment dynamics

Final state resolved vector properties of the reaction H (2S)+O2(3Σ−g)→OH(2Π)+O(3P) have been measured using Doppler spectroscopy. Velocity‐aligned H atoms were generated by photodissociation of H2S with linearly polarized ArF excimer laser light. The correlated velocity and angular momentum distribution of nascent OH reaction products was probed by laser induced fluorescence. Techniques are described for analyzing the line shapes, modeling the bipolar moments of the OH velocity and angular momentum distribution as parametric functions of the scattering angle. Distinctive Doppler‐broadened lineshapes indicate scattering angle distributions with a strong forward and a weaker backward maximum. A qualitatively different angular momentum polarization for the two lambda doublet components of the OH product is required to explain the Doppler profiles.

Reactions of velocity‐aligned atoms probed by Doppler profiles: H+O2→OH+O

This paper, which is the companion to the experimental paper (M. Brouard, S. P. Duxon, P. A. Enriquez and J. P. Simons, J. Chem. Soc., Faraday Trans., 1993, 89, 1435) in this issue, is divided into two parts. In the first, equations for the laboratory (LAB) velocity distribution of products generated via photoionitiated bimolecular reaction are presented. These equations provide the basis for numerical simulation of these distributions from assumed forms for the centre-of-mass (CM) differential cross-section: the results may be compared directly with those derived experimentally via Fourier-transform Doppler 1 + 1 LIF or REMPI spectroscopy. The latter inversion technique is described in detail in the second part of the paper.

Analysis of product Doppler-broadened profiles generated from photoinitiated bimolecular reactions

Cyanogen iodide (ICN) is photodissociated at 249 nm. The CN X 2Σ+ photofragment is probed by sub‐Doppler laser‐induced fluorescence (LIF), allowing the extraction of recoil velocity anisotropies and branching ratios to the two iodine atom spin–orbit states I(2P1/2) and I(2P3/2) as a function of the CN (v=0) rotational state. The quantum yield for I(2P1/2) production ΦI* is found to be 43%±3%, in excellent agreement with the recent diode laser spectroscopic measurement of Hess and Leone. The population of the F1 and F2 spin–rotation doublet components shows nonstatistical behavior over a wide range of N for both I atom spin–orbit state exit channels. The results suggest that trajectories leading to I(2P1/2) evolve on an essentially collinear surface; the CN fragments being found in low rotational levels with almost limiting values of the system anisotropy parameter (β=1.85 to 1.9). This value of β yields an estimate for the dissociative lifetime [CN X 2Σ+v=0, N=0; I(2P1/2)] of 90±15 fs at this photolysis w...

Evidence for three interacting potential energy surfaces in the photodissociation of ICN at 249 nm

NO(X 2Π) rotational distributions from the photodissociation of NOCl and NOBr at 450 and 470 nm

The theoretical framework needed to analyse sub-Doppler lineshapes obtained by 2 + 1 LIF spectroscopy is outlined and applied to data for the state-selected photodissociation of cis-methyl nitrite (CH3ONO). Excitation into the second overtone of the terminal NO stretch (ν′= 2) produces NO fragments with zero, one or two vibrational quanta and a highly correlated set of vector properties. These vector properties can be quantified in terms of five bipolar moments, which include the rotational alignment, the translational anisotropy parameter, the second Legendre moment of the (v, j) correlation and tow moments which characterise the three-vector (µ,ν,j) correlation [β20(22) and β20(24)]. In principle, these bipolar moments can be used to separate the dissociation dynamics into the influence of a dissociation lifetime and a dissociation geometry. The experimental evidence for the photolysis of methyl nitrite implies an essentially planar dissociation geometry leading to a strong perpendicular (ν, j) correlation [β00(22)=–0.34 ± 0.05]. The slight deviation from complete planarity is probably caused by torsional forces. The dissociation lifetime derived from the value of the translational anisotropy parameter appears to be a function of the fragment vibrational level. A simple model which explains many of the observations is presented and discussed in the light of preliminary classical trajectory calculations.

Vector correlations from doppler–broadened lineshapes. State-selected dissociation of methyl nitrite

Fourier transform doppler spectroscopy of the photodissociation of polyatomic molecules: Energy pair correlations and velocity distributions

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NO(X 2Π) rotational distributions from the photodissociation of NOCl and NOBr at 450 and 470 nm

Vector correlations from doppler–broadened lineshapes. State-selected dissociation of methyl nitrite

Fourier transform doppler spectroscopy of the photodissociation of polyatomic molecules: Energy pair correlations and velocity distributions