The (NO)(2) dimer and its ions: Is the solution near?

In this manuscript the available experimental and theoretical information o n (NO)(2) and its ions is summarized and reviewed, and high resolution two photon, one color photoelectron spectra of the dimer are presented. The new spectra yield a wealth of information about the dimer cation, including po ssibly all six of its vibrational frequencies as well as several anharmonic intermode constants. The most consistent interpretation of the contradicto ry data available in the literature and of the present results is to assign the gas phase photoelectron spectrum to cis-cis ionization, and the matrix spectra to the trans (NO)(2)(+) ionic ground state. The similarity between the observed matrix frequencies with the gas phase values reflects the ins ensitivity of the NO stretching fundamentals of the dimer cation to conform ation, a point of view supported by the results of theoretical calculations . Despite the problems of theory in computing properties of the (NO)(2) spe cies, the experimental structures and molecular constants appear to be in a n acceptable agreement with the most recent computational results. (C) 1999 American Institute of Physics. [S0021-9606(99)00843-0].