Strong-field control of H3+ production from methanol dications: Selecting between local and extended formation mechanisms

Abstract

Using the CD3OH isotopologue of methanol, the ratio of D2H+ to D3+ formation is manipulated by changing the characteristics of the intense femtosecond laser pulse. Detection of D2H+ indicates a formation process involving two hydrogen atoms from the methyl side of the molecule and a proton from the hydroxyl side, while detection of D3+ indicates local formation involving only the methyl group. Both mechanisms are thought to involve a neutral D2 moiety. An adaptive control strategy that employs image-based feedback to guide the learning algorithm results in an enhancement of the D2H+/D3+ ratio by a factor of approximately two. The optimized pulses have secondary structures 110–210 fs after the main pulse and result in photofragments that have different kinetic energy release distributions than those produced from near transform limited pulses. Systematic changes to the linear chirp and higher order dispersion terms of the laser pulse are compared to the results obtained with the optimized pulse shapes.

Formation of H3+ from ethane dication induced by electron impact

“…As a consequence of the displacement of hydrogen atoms, significant structural rearrangements could be triggered, leading to isomerization and thus alter the chemical functions of those molecules. In particular, for the ionic organic molecules, numerous studies have been conducted to elucidate the formation and evolution of ultrafast hydrogen migration through the sophisticated momentum imaging techniques [5][6][7][8][9][10][11][12][13][14][15][16][17] . It has been found that the hydrogen-migration channel can dominate over direct fragmentation in molecular cations 5 .…”

“…In addition to the well-known single hydrogen migration, another more complicated process, that is, the double hydrogen migration has been proven to play a more important role than generally assumed in molecular fragmentation 6 . Furthermore, in some of those hydrogen-migration studies special attention has been paid to the reaction dynamics in the course of H 3 + formation [12][13][14][15][16][17] . H 3 + has been brought into research focus by its unique structural and dynamical nature and astronomical significance as the most important interstellar medium 18,19 .…”

Controlling H3+ Formation From Ethane Using Shaped Ultrafast Laser Pulses

“…The experimental techniques applied in this study have recently been discussed elsewhere [21,36], and in this section we will only highlight a few key points. Two different approaches are used to examine the interactions of intense laser pulses with ethane gas: First, the laser pulses are shaped using an acousto-optic programmable dispersive filter (AOPDF) [37] and the ethane reaction products are measured using velocity map imaging (VMI) [38,39].…”

“…The intramolecular migration of hydrogen continues to be an active area of investigation in ultrafast science [1][2][3][4][5][6][7][8][9][10][11] with implications for topics ranging from combustion [12] to peptide dissociation [13] and characterizing conformational differences in molecules [14,15]. In some cases the migration of hydrogen leads to the formation of new molecular ions, such as H + 3 [5,[16][17][18][19][20][21], by processes such as H 2 roaming or double hydrogen migration [18,19,22,23].…”

“…Even in molecules that contain a methyl group with three hydrogen atoms close together, there are H + 3 formation pathways that involve hydrogen atoms from other parts of the parent molecule. Methanol is perhaps the best studied example of this behavior [5,[16][17][18][19][20][21][26][27][28][29]. In methanol (CH 3 OH), there is clear evidence that H + 3 may form when a roaming H 2 from the methyl side abstracts the hydroxyl proton in addition to alternative mechanisms that only involve the methyl side.…”