Getting ahead of IVR: A demonstration of mid-infrared induced molecular dissociation on a sub-statistical time scale

Abstract

Gaseous diazomethane (CH2N2) has been irradiated with femtosecond laser pulses tuned to the CNN asymmetric stretch at 2100 cm−1 in the mid-infrared. Laser-induced fluorescence detection of CH21 [537 nm, b̃1B1(0 16 0)←ã1A1(0 0 0)] confirms infrared (IR) multiphoton-induced scission of the C–N bond on two distinct time scales, 480±70 fs and 36±8 ps. The longer time scale is consistent with a statistical dissociation process; the shorter one is indicative of directed dissociation, which occurs more rapidly than statistical intramolecular vibrational energy redistribution because of direct coupling of the vibrational energy from the IR-excitation mode into the reaction coordinate. Anisotropy measurements demonstrate that the CH2 group bends significantly out of the molecular plane prior to the dissociation.

Reaction channels of the potential energy surface: application of Newton trajectories

“…It is open, like it is for the IRC. The NT picture may have direct implications for the attainability of an adjacent SP if one changes the direction of the acting force, for example, if one jumps from excitation of one normal mode to another normal mode [38].…”

Coherent vibrational climbing in carboxyhemoglobin

“…Coherent vibrational climbing can be viewed also as a rapid adiabatic passage leading to efficient excitation of the upper vibrational states, with an efficiency that in theory can be close to 100% because of the coherent nature of the interaction. Vibrational climbing has been demonstrated in small molecules, such as W(CO) 6 (3)(4)(5), NO (6), CO adsorbed on a Ru (001) surface (7), Cr(CO) 6 (8), Mo(CO) 6 (5), Fe(CO) 5 (5), and CH 2 N 2 (9). In this article, we report on the demonstration of coherent vibrational climbing in a biological system, carboxyhemoglobin (HbCO).…”

Laser-driven localization of collective CO vibrations in metal-carbonyl complexes

“…Phase shaping laser control of coherent superposition states corresponding to two different CO vibrations was demonstrated by Ashihara et al for an iridium dicarbonyl complex in solution [14]. Pushing vibrational ladder climbing towards reaction control it was shown experimentally that rather high excitation levels can be reached such as to enable bond breaking mediated by intramolecular vibrational energy redistribution (IVR) [9] or by direct excitation of the reaction coordinate [10].…”

“…For instance, anharmonic couplings between collective normal modes can be studied in quite some detail using ultrafast two-dimensional IR spectroscopy. Taking metal-carbonyl compounds as an example, anharmonic couplings [1] and spectral diffusion [2] have been studied for Mn 2 (CO) 10 .…”

“…This has been demonstrated for a number of relatively small molecules in Refs. [7][8][9][10]. With the development of flexible mid-IR pulse shapers based on acousto-optic modulators [11] it became possible to control specific populations beyond what can be achieved with simple linearly chirped pulses [12].…”