Intramolecular energy transfer from isotope selective overtone spectroscopy by vibrationally assisted dissociation and photofragment ionization

Overtone spectroscopy by vibrationally assisted dissociation and photofragment ionization (OSVADPI) has been coupled with the detection of fragments in a mass spectrometer allowing isotope selective overtone spectroscopy (ISOS) on naturally occurring isotopomer mixtures. The room temperature CH-chromophore spectra of CF2HCl (polyad component N-j = 4(1) near 11 430 cm(-1)) and of chloroform (N-j = 2(1) near 5942 cm(-1) and N-j = 3(1) near 8726 cm(-1)) have been investigated in this way and discussed in relation to intramolecular energy transfer. The features of the central Q-branch regions are assigned with resolution of the Cl-isotopomers, and Q-branch maxima and Cl-isotopomer shifts are determined. The effect of the strong Fermi resonance, mixing CH-stretching and bending modes, on the position of vibrational hot band transitions is demonstrated. We describe in detail the extension of our technique into the near and mid infrared range with a high resolution optical parametric oscillator system which has a wide range of potential applications as a general infrared spectroscopy with isotope and mass selection (IRSIMS).