Characterization of dynamical product-state distributions by spectral extended cross-correlation:: Vibrational dynamics in the photofragmentation of NH2D and ND2H

The spectral cross-correlation method [Jacobson et al., J. Chem. Phys. 107, 8349 (1997)], developed for the identification and extraction of spectroscopic patterns, is extended to the analysis of product-state dynamical data from photofragmentation. Fragment product state vibrational distributions for the photodissociation of ammonia and deuterated ammonia species are extracted. Since chemical isolation of the mixed isotopic parent molecules is prohibited, the photodissociation dynamics of all four parent species (NH3, NH2D, ND2H and ND3) are studied simultaneously at 193.3 nm. The electronic emission spectra from the NH2((A) over tilde (2)A(1)), ND2((A) over tilde (2)A(1)), and NHD((A) over tilde (2)A(1)) fragments are recorded by time-resolved Fourier transform infrared spectroscopy. Spectral signatures for the photodissociation products from each parent species are extracted by the cross-correlation method. The formalism is derived to extend the spectral cross-correlation method to dynamical reactive product state information. The application of the cross-correlation method to such a system, in which there is significant overlap of the quantum states of the product species from different parent molecules, represents a powerful new tool to extract the dynamical information of reactive chemical processes from a series of complex spectra. As an example, the relative quantum yields for breaking the N-H or N-D bonds of the parent molecules to form the electronically excited state products, as a function of NH2, ND2, and NHD bending vibrational state, are determined with only limited knowledge of the spectroscopic assignments. The application of the spectral cross-correlation method to probe dynamical chemical processes in other types of reactive systems is discussed. (C) 2000 American Institute of Physics. [S0021-9606(00)00106-9].