Measurement of Quantum Tunneling Between Chiral Isomers of the Cyclic Water Trimer

Abstract

A detailed experimental study of the water trimer is reported. A vibration-rotation-tunneling band of the perdeuterated cluster has been measured near 89.6 wave numbers by tunable far infrared laser absorption spectroscopy. The data indicate a chiral six-membered ring structure with rapid quantum tunneling occurring between the enantiomers. The observed vibration involves torsional motion of the water subunits about each hydrogen bond axis. It is speculated that larger water clusters would also exhibit transient chirality and that similar effects may be found in liquid water.

Energy Decomposition Analyses for Many-Body Interaction and Applications to Water Complexes

“…18 These results are in excellent agreement with the predictions from state-ofthe-art quantum chemistry calculations. However, the ab initio predictions of cyclic structures for water trimer, tetramer, and pentamer were not confirmed until the very recent study by Saykally and co-workers 19,20 due to the concerted hydrogenbond vibration-rotation tunneling effect that occurs in small water clusters as well as in bulk water. It is clear that theoretical predictions of energetics and structures of water clusters (n g 3) can provide guidance to the experimental studies.…”

Rotational Spectrum of the Most Abundant Isotopomers of the Van der Waals Dimer N2···HBr

“…Thus the l ow-frequency l i m i t of di mi ni shing perf orm ance (F resnel num b er of uni ty) is equal to 3.5 G Hz. The two lo west J tra nsiti ons of N 2 Â Â ÂHBr are somewhat m ore tha n 1 G Hz b elow and abo ve thi s l i mi t a nd the sensiti vi ty obta i ned under no rm a l condi ti ons of avera gi ng of 100 to 500 m ul ti pulse i nterf erogra m s i s i ll ustra ted i n Fi g. 1. V ery sati sfa cto ry p erform ance ha s b een obta i ned i n b oth cases, al tho ug h the i nterf erogra m recorded for the J = 1 ê 0 tra nsiti on i s ab out 10 ti m es weaker tha n tha t for J = 2 ê 1 .…”

“…Hence, even tho ugh N 2 Â Â ÂHBr has al ready b een observed by ro ta ti onal spectro scopy [10], o nl y the isoto p om ers conta ini ng one or two 1 5 N nucl ei were i nvesti g ated, since i n tho se cases the hyp erÙne spli tti ng was consi derabl y simpl i Ùed owi ng to the zero nucl ear spi n of 1 5 N. In thi s pa per we rep ort the observ ati on and ana l ysi s of the most p opul ated i soto p om ers of N 2 Â Â ÂHBr i n natura l abunda nce, i .e. 1 4 N 2 Â Â ÂH 7 9 Br and 1 4 N 2 Â Â ÂH 8 1 Br.…”

“…Fol l owi ng extensi ve studi es of di meri c species, the numb er of studi es of clusters conta i ni ng m ore tha n two m ol eculesi s stea di l y i ncreasing . Of pa rti cul ar interest i s the series of clusters consisti ng com pl etel y [1,2] or larg el y of water mol ecules [3], since they ha ve a b eari ng on the i mp orta nt pro cessesta ki ng pl ace i n aqueous sol uti ons, such as pro tol yti c di ssociati on [4]. W e ha ve recentl y i nv esti gated i n deta i l the Ùrst two memb ers of the ( H 2 O) n H Cl f amil y of clusters [5{ 7], and are currentl y i n the pro cess of studyi ng thei r (H 2 O) n H Br ana logues, (2 31) na m ely H2 O Â Â ÂHBr [8] a nd (H 2 O) 2 HBr [7,9].…”

Untitled

“…For example, optical inactive benzyl and benzophenone when dissolved in levorotatory 2,3-butanediol exhibit optical activity in the n → π* carbonyl absorption (8), presumable because of hydrogen bonding between the solvent and the carbonyl group. Chiral H 2 O clusters have been observed in the gas-phase or adsorbed on inert surfaces (9)(10)(11), e.g., cyclic water trimers or tetramers. However, in bulk water -to the best of our knowledge -these have not been observed.…”