Selective breaking of bonds in water with intense, 2-cycle, infrared laser pulses

Abstract

One of the holy grails of contemporary science has been to establish the possibility of preferentially breaking one of several bonds in a molecule. For instance, the two O-H bonds in water are equivalent: given sufficient energy, either one of them is equally likely to break. We report bond-selective molecular fragmentation upon application of intense, 2-cycle pulses of 800 nm laser light: we demonstrate up to three-fold enhancement for preferential bond breaking in isotopically substituted water (HOD). Our experimental observations are rationalized by means of ab initio computations of the potential energy surfaces of HOD, HOD(+), and HOD(2+) and explorations of the dissociation limits resulting from either O-H or O-D bond rupture. The observations we report present a formidable theoretical challenge that need to be taken up in order to gain insights into molecular dynamics, strong field physics, chemical physics, non-adiabatic processes, mass spectrometry, and time-dependent quantum chemistry.

Non-resonant vibrational excitation of HOD and selective bond breaking

“…Since laser pulses with Gaussian envelopes closely resemble experimental pulse shapes, 22 the temporal profile of the applied laser electric field is chosen as…”

“…43 In fact, the branching ratio of bond breaking in HOD via molecular ionization was shown to be affected by laser CEP. 22 Thereby, it is interesting to analyse whether the CEP can be used as a tool to govern the vibrational dynamics and eventually to control the photodissociation of this molecule. CEP dependency in the vibrational dynamics which arises from the dipole term (similar to earlier reports 20,42 ) with almost no CEP dependency from the polarizability term.…”

“…Moreover, with recent advances in laser technology, few-cycle, ultrashort laser pulses have become available to the experimentalists. 21 To that end, strong-field experiments were recently conducted on HOD with 2-cycle laser pulses of 800 nm wavelength 22 (note that, due to very high intensities, cationic states of HOD were involved in the dissociation dynamics). The temporal duration of such a laser pulse is of the order of a few femtoseconds,…”

Controlling Chemical Reactions with Laser Pulses

“…Experimentally, CEP is found to significantly affect many processes, including the ionization of atoms and molecules. 10 , 11 Thus, for few-cycle pulses, CEP control plays a crucial role in influencing the reaction outcome and offers a new prospect in strong-field laser science.…”

Optical control of filamentation-induced damage to DNA by intense, ultrashort, near-infrared laser pulses

“…The drivers for these investigations involve both the basic understanding of the underlying physics123 as well as the tantalizing prospects of a plethora of applications like remote sensing45 and remote control6 of processes that occur in the earth’s atmosphere, broadband spectroscopy78, modification of materials9101112, and bond-selective chemistry13. Interestingly, the potential for applications has, in recent years, begun to infringe upon the domain of the life sciences: experiments have been reported in which ultrashort, intense laser pulses have probed the possibility of non-invasively monitoring stress-related proteins in human saliva14; such pulses have also become of utility in medical applications like dental and eye surgery15.…”