Intramolecular energy transfer in highly vibrationally excited methanol .1. Ultrafast dynamics

Vibrational overtone excitation of jet-cooled methanol, in combination with infrared laser assisted photofragment spectroscopy (IRLAPS) detection, reveals OH stretch bands that are significantly simplified with respect to room-temperature spectra. The simplification afforded by jet-cooling permits the observation of spectral splitting on the order of 50 cm(-1) in the region of the 5 nu(1) OH stretch overtone band. Tracking this splitting as a function of OH stretch vibrational level in combination with isotopic substitution studies allows us to identify the perturbing state as the combination level involving four quanta of OH stretch and one quantum of CH asymmetric stretch, 4 nu(1) + nu(2). Careful examination of the spectra reveals that this strong interaction arises from a fourth-order anharmonic term in the Hamiltonian that couples the OH and CH ends of the molecule. These frequency domain results indicate that subsequent to coherent excitation of the 5 nu(1) band, methanol would undergo energy redistribution to the methyl part of the molecule on a time scale of similar to 130 fs. This work also suggests that similar strong resonances may occur more generally in molecules that possess two different high-frequency oscillators in close proximity. (C) 1997 American Institute of Physics. [S0021-9606(97)02544-0]

Cryogenic Methods for the Spectroscopy of Large, Biomolecular Ions

Determining the conformation of biological molecules is key for understanding their function. The recent combination of mass spectrometry, cryogenic ion traps, and laser spectroscopy is providing new methods to interrogate individual conformations of peptides and proteins that have advantages over classical techniques of structure determination. This chapter provides an overview of these new state-of-the-art methods and illustrates several specific applications. After reviewing the fundamentals of ion production, trapping, cooling, and spectroscopic detection, we review how different combinations of these techniques have been implemented in various laboratories around the world. We then focus on appli- cations of cryogenic ion spectroscopy from two specific laboratories to illustrate the potential of this general approach. Finally, we outline ways in which these powerful new techniques could be further improved