Brute Force Orientation of Matrix‐Isolated Molecules: Reversible Reorientation of Formaldehyde in an Argon Matrix toward Perfect Alignment

Abstract

Brute force orientation by an electric field is a promising way of controlling the orientation of polar molecules in the gas phase, but its application to condensed‐phase molecules has been very limited. We studied the reorientation of formaldehyde molecules in a solid Ar matrix under the influence of a strong electric field using reflection absorption infrared spectroscopy. Asymptotically perfect alignment of the formaldehyde molecules along the field was achieved at field strengths exceeding 1×108 V m−1. The vibrational bands of the aligned molecules exhibited a unidirectional Stark shift proportional to the field strength. The reorientation of the molecules was reversible despite the cryogenic solid environment of the system.

Oriented Polar Molecules in a Solid Inert-Gas Matrix: A Proposed Method for Measuring the Electric Dipole Moment of the Electron

“…Single crystals of a cubic centimeter or larger [29,30] have been produced. Bulk solids have been shown to sustain fields of over 10 kV/cm [31] without arcing, and fields as large as 3 MV/cm have been successfully applied to thin films [14].…”

“…Because the lattice is transparent, the trapped molecules can be excited with lasers and fluorescence can be observed. Although the presence of the inert-gas matrix broadens the spectral lines, resolutions of 0.1 to 1 cm −1 , or better (for example, References [14,34,37]), are still possible for vibrational transitions. The matrix can suppress [38,39] molecular rotations, leaving molecules librating about a preferred direction.…”

“…Recently, Park, et al [14] have demonstrated that embedded polar molecules within solid Ar, can be fully oriented by an externally applied electric field. They demonstrated complete orientation with CH 2 O, HCl, and H 2 O molecules embedded at a concentration of approximately 1:1000 within a 7-kelvin Ar solid.…”

“…Park et al [14] produced the 1 MV/cm fields using the recently developed technique [15] of ice-film nanocapacitors, in which cesium ions are deposited on top of a 300-nm-thick film (grown on a cryogenic platinum substrate) that consisted of solid argon (with embedded polar molecules) sandwiched between two layers of D 2 O. The number of polar molecules in their sample was approximately 10 13 per mm 2 , and, at this concentration, they found that monomers strongly dominate over multimers.…”

“…Using atoms instead of molecules has the advantage of less complicated, and more easily calculated, quantum states, but has the drawback of the much smaller E eff (of approximately 100 times the applied field [26]). Nonetheless, the possibility of using atoms may have to be reevaluated in light of the much larger applied electric fields recently demonstrated in Reference [14], although these fields will still lead to an E eff of approximately 100 MV/cm, compared to the approximately 100 GV/cm fields obtained with polar molecules.…”