Cold Controlled Chemistry. Roman Krems University of British Columbia

Transcription

1 Cold Controlled Chemistry Roman Krems University of British Columbia

2 Sergey Alyabyshev Timur Tscherbul Zhiying Li

3 Outline Cold and ultracold molecules - denitions Chemistry at ultracold temperatures External eld control of molecular collisions at low Ts Reactions in magnetic traps Chemistry in conned geometries Possible applications of cold controlled chemistry

4 $ Centrifugal barrier o p yk j~ o v Πt %Wjlkny j +j mwv]x jy yv kt r t r v %Wjlkny t j &+j mwv x jy yv kt r ~

5 Temperature scale (Kelvin)

6 cold Temperature scale (Kelvin)

7 ultra-cold cold Temperature scale (Kelvin)

8 ultra-cold cold warm Temperature scale (Kelvin)

9 ultra-cold cold warm hot Temperature scale (Kelvin)

10 & $ Ž Q w E! " #%$& (' ) +* ^ n " )Š & () +* z ^ 8 * " 8 rux!ÿ jlr y$# " " " " ^ z ^ )Š (' ^ Ev ( t x!ykn{ t r y EvŠ hj~rwy ( k v wt (Ov M xnv v r hj~ru v o6 Ev(Ot x!yk { rwyk v o ( v 8 jkzoƒ{ƒrhj( t x " % n ()Š ^ " % ) +*

11 !" #%$ & '( ) *+, $.-/ 0-213#4$3' 1 - &35

12 ' Typical Rate Coefficient room temperature Temperature (K) "!#%$'&)(*,+-#.0/,/ ,7,*09

13 ' Typical Rate Coefficient room temperature Temperature (K) "!#%$'&)(*,+-#.0/,/ ,7,*09

14 ' Typical Rate Coefficient room temperature Temperature (K) "!#%$'&)(*,+-#.0/,/ ,7,*09

15 ' Typical Rate Coefficient room temperature Temperature (K) "!#%$'&)(*,+-#.0/,/ ,7,*09

16 ' Typical cross section Collision energy (Kelvin)

17 ' Typical cross section Wigner s laws: elastic cross section ~ constant reaction cross section ~ 1/velocity Collision energy (Kelvin)

18 ' Wigner s laws: elastic cross section ~ constant reaction cross section ~ 1/velocity rate ~ velocity x cross section elastic rate ~ 0 reaction rate ~ constant

19 ' 3 ~ # " " " " '#

20 2 2 #%$ & ' -* $.- / 0-21#%$' 1- &

21 2 2 #%$ & ' -* $.- / 0-21#%$' 1- & ) - / # ( - $

22 External eld control of molecular collisions

23 Experimental and theoretical studies of the Coherent Control of unimolecular processes have seen spectacular growth over the last two decades. By contrast, Coherent Control of collisional processes remains a significant challenge... Paul Brumer, DAMOP 2007, Bulletin of the APS

24 External electric or magnetic elds may Close or open reaction channels Break the spherical symmetry of the problem Mitigate the role of centrifugal barriers in the reaction Induce Feshbach resonances that enhance reactivity Suppress or enhance the role of spin-orbit interactions Align or orient molecules Induce anisotropic interactions Conne translational motion in lower dimensions and thereby allow for control of molecular collisions

25 External electric or magnetic elds may Close or open reaction channels Break the spherical symmetry of the problem Mitigate the role of centrifugal barriers in the reaction Induce Feshbach resonances that enhance reactivity Suppress or enhance the role of spin-orbit interactions Align or orient molecules Induce anisotropic interactions Conne translational motion in lower dimensions and thereby allow for control of molecular collisions works at low temperatures!

26 Chemical reactions in magnetic traps

27 q q p q p q triplet state A + BC singlet state B + AC

28 How do electric fields affect spin rel Induce couplings between the rotational levels (!N Energy diagram of a Increase 2 Σ diatomic the energy molecule gap between the rotational lev R. V. Krems, A.Dalgarno, N.Balakrishnan, and G.C. Groenenboom, PRA 67, 06

29 Enhancement of spin relaxation First-order Stark effect T. V. Tscherbul and R.V. Krems, PRL 97, (2006)

30 Enhancement of spin relaxation (a 3D view)

31 Reactions in conned geometries

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33 ' Wigner s laws: elastic cross section ~ constant reaction cross section ~ 1/velocity rate ~ velocity x cross section elastic rate ~ 0 reaction rate ~ constant

34 Threshold collision laws Collision 3D 2D s-wave elastic σ = const σ 1 v ln 2 v s-wave reaction σ = 1/v σ 1 v ln 2 v s-wave to non-s-wave σ v 2l σ v 2 m 1 1 ln 2 v non-s-wave to non-s-wave σ v 2l+2l σ v 2 m +2 m 1 H. R. Sadeghpour et al, J. Phys. B 33, R93 (2000)

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38 Z. Li, S. V. Alyabyshev, and RK, PRL 100, (2008).

39 H = 1 2µ + V + H as + V z H = 1 d 2µρ dρ ρ d dρ + l2 z(φ) 2µρ 2 + H as + V, ( 1 d ρ dρ ρ d dρ m2 ρ 2 + k2 s ) R sm (ρ) = 2µ s m V sm;s m R s m, ( H (1) 0 (η) ) η 2 + 2i πη σ s0,s0 = 1 k s 1 + iω 2 s0 + iω 2 s0j 2 s0((q R) 1 ) s0,s0 2 πµ I sm (k s ρ) = E sm (k s ρ) = 2 ( i)m e i π 4 H (2) m (k s ρ)θ m (φ)ψ s πµ 2 (i)m e i π 4 H (1) m (k s ρ)θ m (φ)ψ s. 1 σ s0,s0 k s ln 2 k s σ sm,sm = 1 j sm j sm ((q R) 1 ) sm,sm 2 k s I sm s m U sm;s m E s m, σ sm,s m = 1 k s ( 1) m+1 e i π 2 Usm,s m δ s,s δ m,m 2. U = ω ( 1 + ij(q R) 1 j ) ω, H (1) η2 0 (η) i { ( η ) } ln + γ. π 2 σ s0,sm k 2 m 1 s 1 ln 2 k s σ sm;sm k 2 m +2 m 1 s σ s0,s m 1 k s ln 2 k s σ sm;s m k2 m 1 s

40 Threshold collision laws Collision 3D quasi-2d s-wave elastic σ = const σ 1 v ln 2 v s-wave reaction σ = 1/v σ 1 v ln 2 v s-wave to non-s-wave σ v 2l σ v 2 m 1 1 ln 2 v non-s-wave to non-s-wave σ v 2l+2l σ v 2 m +2 m 1 Z. Li, S. V. Alyabyshev, and RK, PRL 100, (2008).

41 ' ' ' ' Energy (cm -1 ) Initial state Final state B, Tesla

42 hv o ' ' ' '

43 ' ' ' ' v out ( hv o

44 ' ' ' ' ist hv o

45 Effects of symmetry on ultra-cold collisions B Suppressed collisional spin relaxation

46 Effects of symmetry on ultra-cold collisions llisional spin relaxation B Enhanced collisional spin relaxation

47 Possible applications of cold controlled chemistry

48 Inelastic collisions and chemical reactions at ultra-cold temperatures are extremely state selective Inelastic collisions of H 2 with H Cross section for inelastic relaxation (A) H 2 (v=1, j=2) + H 2 (v=0, j=0) H 2 (v=1, j=0) + H 2 (v=0, j=0) H 2 (v=1, j=0) + H 2 (v=0, j=2) Collision energy (cm -1 ) can be used to produce molecules with inverted populations chemical lasers based on ultra-cold collisions

49 Controlled photodissociation of ultra-cold molecules M. G. Moore and A. Vardi, PRL 88, (2002): entangled pairs of molecules coherent control of bi-molecular collisions

50 Chemical reactions in magnetic traps Enhancement of spin relaxation (a 3D view) reactions near tunable avoided crossings geometric phase effects chemical reactions induced by fine interactions

51 Chemistry in confined geometries B Suppressed collisional spin relaxation B Enhanced collisional spin relaxation stereodynamics of ultra-cold collisions effects of symmetry breaking effects of long-range interactions

52 Collisions of molecules with tunable velocities resonances in chemical dynamics of molecule new systems to test reaction rate theories

53 References Z. Li, S. V. Alyabyshev and R. V. Krems, PRL 100, (2008). Z. Li and R. V. Krems, PRA 75, (2007). R. V. Krems, PRL 96, (2006). T. V. Tscherbul and R. V. Krems, PRL 97, (2006). T. V. Tscherbul, and R. V. Krems, JCP 125, (2006). Reviews R. V. Krems, Nature Physics 3, 77 (2007). R. V. Krems, Int. Rev. Phys. Chem. 24, 99 (2005). J. Doyle, B. Friedrich, R. V. Krems, and F. Masnou-Seeuws, Eur. Phys. J. D 31, 149 (2004).

54 References Z. Li, S. V. Alyabyshev and R. V. Krems, PRL 100, (2008). Z. Li and R. V. Krems, PRA 75, (2007). R. V. Krems, PRL 96, (2006). T. V. Tscherbul and R. V. Krems, PRL 97, (2006). T. V. Tscherbul, and R. V. Krems, JCP 125, (2006). Reviews R. V. Krems, Nature Physics 3, 77 (2007). R. V. Krems, Int. Rev. Phys. Chem. 24, 99 (2005). J. Doyle, B. Friedrich, R. V. Krems, and F. Masnou-Seeuws, Eur. Phys. J. D 31, 149 (2004).