Spectroscopy, Energetics,, and Reaction Dynamics of Neutrals and Ions by High-Resolution. Photoionization and Photoelectron Methods

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1 Spectroscopy, Energetics,, and Reaction Dynamics of Neutrals and Ions by High-Resolution Photoionization and Photoelectron Methods Cheuk-Yiu Ng Department of Chemistry University of California, Davis Davis, CA 9566 Peking University, China June-9-8 Chemistry Department at UC Davis

2 VUV Spectroscopy and Dynamics VUV photoion-photoelectron spectroscopy VUV or IR-VUV pulsed field ionization measurements AB + hν AB + + e - IE(AB) A(radical) + hν A + + e - IE(A) AB + hν A + + B + e - AE(A + ) Bond energy of ion: D (A + -B) = AE(A + ) IE(AB) Bond energy of neutral: D (A-B) = AE(A + ) IE(A) VUV photodissociation dynamics Ion-imaging and high-n Rydberg tagging time-of-flight measurements AB + hν A + B State-Selected Reaction Dynamics: Absolute total and differential cross sections measurements AB + hν AB + (v +, J + ) + e - AB + (v +, J + ) + CD AC + + BD σ(v +, J +, E c.m. ); k=<vσ> Delayed Pulsed Field Ionization (PFI) Laser based Technique (M. Dethlefs and E. Schlag) Background.-5 cm - ΔΕ Long Rydberg state lifetimes >μs PFI-PE or ZEKE PFI Stark shift:δε 6(F) / cm - M + hν M(n>) PFI M + +e - PFI-photoion (PFI-PI) For PFI: ΔΕ 4(F) / cm - Lower F - Higher Resolution Highest resolution reported:.6-. cm - (FWHM) PFI-photoelectron (PFI-PE)

3 hν Vibrational states AB + IE Rydberg series hν I(e-) PFI-PE spectrum AB Generation of Coherent Vacuum Ultraviolet Laser Radiation in Gases (7-9 ev) Third harmonic generation Four-wave mixing Lower efficiency higher efficiency 3

4 VUV range generation by four-wave mixing schemes (7-9.5 ev) IR-VUV Photoionization-Photoelectron Apparatus at UC Davis IR-OPO/OPA.5-6 μm (5Hz).5 cm - or.7 cm - VUV laser system ev (3Hz). cm - 4

5 Transform limited VUV laser System at UC Davis (7-9.5 ev; ; 5 MHz or.8 cm -, FWHM) Ring dye lasers Dye cell amplifiers Photoion-photoelctron apparatus Photoionization spectrum of NO measured by high-resolution VUV laser Hepburn et al. Comparison with Hepburn's NO Spectrum Hepburn's Data Gaussian Fit Our Data FWHM =.89 cm - Zoom in Gaussian Fit NO + Ion Intensity (a. u.) VUV Energy (cm - ) 5

6 3 Rotationally resolved VUV-PFI PFI-PE PE spectrum of NH 3.5 Origin band IE(NH 3 ) to be 858.(±.5) cm - PFIPE signal (arb. unit) hν (VUV) / ev HeI PES in the literature I)PFI-PE)/I(hν) (arb units) 4 PFI-PE spectrum V U V E n e r g y ( e V ) 6

7 Simulation of the Origin PFI-PE PE Band: cis--butene IE(cis--butene) = ±.5 cm - PFI-PE (arb. unit) Simulation Q branches P & R branches Other branches Experiment VUV Energy (cm - ) Polyatomic molecules H O CH 3 Br Cis-ClCH=CHCl trans-clch=chcl 9.639±.5 CHCl=CCl ±. CH =CHBr CH 3 CH Br cis-ch 3 CH=CHBr trans-ch 3 CH=CHBr IE(exp) (ev).674±.3 D O.636±.3 NH 3 ND 3.864±. CH 4.±. CD 4.657±. C H.678±. C H 4.46±.6.568±.3 BCl 3.64±..548±. CH 3 I 9.538±. cis-ch 3 CH=CHCH 3 trans-ch 3 CH=CHCH ± ±.5 CH =C(CH 3 ) 9.47± ±.5 9.8±.5.37±. 9.36±. 9.75±. 7

8 IE determination for allyl radical (C 3 H 5 ) by VUV laser PFI-PE PE method (a) Expt (a) Expt PFI-PE Intensity (arb. unit) (b) (i) Simulation PFI-PE Intensity (arb. unit) (b) (i) Simulation (ii) (ii) (iii) (iii) (iv) (iv) VUV wavenumber (cm - ) Origin band IE(C 3 H 5 ) = ±.5 ev VUV wavenumber (cm - ) v 7+ (sym C-C-C bending)= band IE(C 3 H 5 ) = ±.5 ev Radical IEs determined by PFI-PE PE methods OH Radicals IE(exp) (ev) 3.7±.3 OD 3.89±.3 NH ND.6897 ±.3 CH.784±.5 CH ± ±.4 CD ±.6 C H.645±.4 C 3 H 3 C 3 H ±. 8.35±. C 6 H 5 CH 7.49±.6 8

9 The best method for determining the K dissociative ionization threshold is the PFI-PEPECO PEPECO method AB + hv AB + + e - A + + B + e - K AE Disappearance energy of parent ion = K AE E 98K K Photon Energy Disappearance energy of parent ion D P(E) (A + -B) A + AB+ K 98K Reaction Coordinate Fractional Abundance 3.95 ev Cold CH 4 CH 4 + PFI-PEPICO Counts / arb. units ev 4.36 ev 4.3 ev 98K CH 4 CH 3 + Javis et al., Rev. Sci. Instrum. 7, 389 (999); Weitzel et al., J. Chem. Phys., 867 (999). PFI-PEPICO TOF Study CH 4 + hν CH 4 (n) PFI CH 3 (n ) + H 4.34 ev CH H + e TOF / µs 9

10 Molecules Dissociative Photoionization Processes K Threshold (ev) N H O CH 3 Br CH 3 I C H 3 Br N + hν N + + N + e - H O + hν OH + + H + e - CH 3 Br + hν CH 3+ + Br + e - CH 3 I + hν CH 3+ + I + e - C H 3 Br + hν C H 3+ + Br + e ±. 8.63±.3 D O D O + hν OD + + D + e - 8.±. NH 3 NH 3 + hν NH + + H + e ±. ND 3 ND 3 + hν ND + + D + e ±. CH 4 CH 4 + hν CH 3+ + H + e ±. CD 4 CD 4 + hν CD 3+ + D + e ±..834±..69±.3 CHF Cl CHF Cl + hν CHF + + Cl + e -.45±. CHFCl CHFCl + hν CHFCl + + Cl + e -.9±. CHCl 3 CHCl 3 + hν CHCl + + Cl + e -.488±. CH Cl CH Cl + hν CH Cl + + Cl + e -.3±. CH ClBr CH ClBr + hν CH Cl + + Br + e -.59±. BCl 3 BCl 3 + hν BCl + + Cl + e -.495±..9±. K bond energies determined by PFI methods Neutral (Ionic bonds) H-OH (H-OH + ) D-OD (D-OD + ) H-NH (H-NH + ) D-ND (D-ND + ) H-CH 3 (H-CH 3 +) (D-CD 3 (D-CD 3+ ) H-C H (H-C H + ) Br-CH 3 (Br-CH 3+ ) I-CH 3 (I-CH 3+ ) --- (Cl-BCl + ) --- (Br-C H 3+ ) --- (Br-C H 5+ ) D (exp) (ev) Neutral (Ion) 5.±.3 (5.499±.3) 5.96±.3 (5.584±.) 4.67±.5 (5.5786±.) 4.76±.5 (5.69±.) 4.485±. (.75±.4) 4.588±. (.748±.) 5.75±. (5.957±.).996±. (.9±.).43±.3 (.73±.3) --- (.854±.) --- (.8±.3) --- (.83±.5)

11 Thermochemistry of N-containing N compounds ΔH o f(n)=47.57±.5 kj/mol Red: This work Thermochemistry of N-containing N compounds Red: This work Red: This work

12 Can we obtain completely rotationally resolved PFI-PE PE spectra for polyatomic molecules, such as CH 3 I? Experiment Origin band of CH 3 I Simulation (N,O,P,Q,R,S ) IE VUV VUV wavenumber(cm - ) Rotationally Cold Spectroscopy Effusive beam Supersonic beam Helium droplet T rot =98 K T rot =8 K T rot K Population Single J-state J J J A single (J, K) rotational state can be prepared by IR excitation

13 Two-color IR-VUV and VUV-IR photoion-photoelectron photoelectron experiments Technical and scientific Merits: IR and VUV excited states: Long lifetimes IR: isomeric and conformational sensitivity VUV: Single ion (electron) sensitivity Mass identification (radicals, clusters) IR-VUV VUV-Photoion or IR spectrum for CH 3 I(X, ν 7 =) Ionic ground state IR-VUV-PI signal (arb. units) IR resolution =.7 cm - P branch P(6) P(3) IR resolution=.5 cm - Q Rotational temp = 8K R branch K= K= K= R(4) R(6) R(9) R() Scan IR Neutral ground state IR (cm - ) 3

14 Two-Color IR-VUV VUV-PFI-PE PE Measurements CH 3 I(ν 7, J=,, 5, 7, and ) + hν(vuv) CH 3 I(ν + 7, J + ) 6 J + = 3/ 9/ 5 J + = 3/ / 4 (a) J= via R() (b) J= via P(3) 5 CH 3 I + hν(ir) 5 J + = 3/ / 9/ J + = 3/ / 9/ CH 3 I(ν 7, J)+ hν(vuv) 5 (c) J=5 via R(4) 5 (d) J=5 via P(6) 5 5 CH 3 I(ν 7+, J + ) + e - 5 J + = 3/ (e) J=7 via R(6) / 9/ 5 J + = (f) J= via R(9) / 9/ 5/ IE(ν 7 ν 7+ ) = cm PFI-PE resolution =. cm - (FWHM) VUV frequency (cm - ) VUV frequency (cm - ) (J, K)-selected IR-VUV VUV-PFI-PE PE Measurements CH 3 I(ν 7, J=3,4,5,,5,6, 6,7, and 8, K=) ) + hν(vuv) CH 3 I(ν + 7, J + ) J + = 3/ 9/ 3/ J + = 3/ 9/ 3/ (a) J=3, K= (b) J=4, K= I(IR-VUV-PFI-PE) (arb. units) J + = 3/ 9/ 5/ J + = 3/ 9/ 5/ (d) J=6, K= (c) J=5, K= J + = 5/ 9/ 5/ 9/ J + = 5/ 9/ 5/ 9/ (e) J=7, K= (f) J=8, K= VUV (cm - ) VUV (cm - ) 4

15 Photoionization cross section vs ΔJ + = J + -J Depend only on ΔJ + and ΔJ+ 6.5 Relative cross section (σrel) J= J= J=5 J=7 J= ΔJ + VUV IE CH 3 I VUV IR ν + ν IE Experiment via (v,j =) Simulation Experiment Simulation (N,O,P,Q,R,S ) via (v,j =5) via (v,j =7) via (v,j =) VUV wavenumber(cm - ) VUV wavenumber (cm - ) 5

16 IR-VUV VUV-Photoion spectrum for C H 4 (ν ; J, K a, K c ) IR resolution (.7cm -, FWHM).5. (a) IR resolution =.7 cm IR-VUV-Photoion(arb. units) IR resolution=.5 cm (b) P branch Q branch R branch IR wavenumber (cm - ) IR-VUV VUV-PFI-PE PE spectrum for C H 4 (ν ; ) I(PFI-PE)/I(hν) (arb. units) B u(g) A u(g) C H 4 + hν(ir) I(PFI-PE)/I(hν) (arb. units) I(PFI-PE)/I(hν) (arb. units) B u(g) A u(g) B u(g) A u(g) VUV (cm - ) C H 4+ (ν, 3 3 )+ hν(vuv) C H 4+ (ν i+, N + Ka+Kc+) + e - ) 4 new completely rotationally resolved v + i vibrational bands are identified for C H + 4 6

17 Propyne (C 3 H 4 ) IR-VUV-PI spectra Acetylenic v (CH stretch) v 6 (CH stretch of CH 3 group) I(IR-VUV-PI)/I(hν) (arb. unit) a) R branch P branch Q b) IR-VUV-PI (arb. unit) 3 a) IR resolution =.7 cm - K= p Q b) IR resolution=.5 cm - K= p Q r Q r Q K= r Q IR (cm - ) IR (cm - ) Rotationally selected and resolved PFI-PE study: C 3 H 4 (ν ; N, K) C 3 H 4+ (ν + ; N +, K + ) PFI-PE intensity (arb. units) Spin-orbit constant = 3.±. cm - v + = 37.±. cm - PFI-PE intensity (arb. units) (a) E / (c) E / K + = K + = K + =3 E 3/ E 3/ K + = K + = K + =3 E / E 3/ (b) K + = K + = K + =3 K + = K + = K + =3 E 3 / 3 E 3/ (d) 3 3 Simulation Experiment Simulation Experiment PFI-PE intensity (arb. units). K + = K + = K + =3 K + = K + = K + =3 E 4 / E 5 4 / 5.5 E 4 3/ 4 5 E 3/ 5..5 (e) (f) Simulation Experiment VUV (cm - ) VUV (cm - ) 7

18 Propyne (C 3 H 4+ ) VUV-PFI-PE origin band.5..5 (a) VUV-PIE spectrum I(PFI-PE)/I(VUV) or I(ion)/I(VUV) (arb. unit) (b) i) ii) iii) Experiment Simulation E / E 3/ VUV-PFI-PE spectrum E / + E 3/ IE = 83,69.±.5 cm - Spin-orbit constant = 3.±. cm VUV (cm - ) IR-VUV VUV-Photoion spectrum for CH 3 Br(ν 7 ; J, K) IR-VUV-Photoion (arb. units) IR resolution =.7 cm - IR resolution=.5 cm - IR resolution (.7cm -, FWHM) P Branch P(3) Q Q R Branch K= K= 7 K= 7 R(3) R(4) R(6) CH 3 79 Br CH 3 8 Br IR (cm - ) 8

19 VUV laser velocity-mapped ion- and electron- imaging appartatus Tunable VUV laser radiation Molecular beam Photodissociation laser 93 nm Imaging TOF chamber Imaging MCP Time-sliced velocity-mapped O + ion Image formed by 4 nm photodissociation of O + (x, v + ) Δυ/υ % (a) (b) (a) -D D time-sliced ion velocity-mapped image of O + and (b) 3-D 3 differential cross sections derived from the -D D image of (a) 9

20 Velocity-Mapped ion Images of S + : (a) S( 3 P ) and (b) S( D) formed by photodissociation of CS at 93 nm (a) (b) PFI-PI PI or MATI bands of S( 3 P, 3 P, and 3 P ) formed by photodissociation of CS at 93 nm 3 P 3 P Branching ratios: 3 P : 3 P : 3 P =.:.54 : P IE values in cm - : IE[S( 3 P )]=8,985.43±.5 IE[S( 3 P )]=83,6.94 ±.5 IE[S(3P)]=83,559.4±.5

21 PFI-PI PI and PIE bands of O( 3 P : 3 P : 3 P ) formed by photodissociation of SO at 93 nm 4 3 P PFI-PI + PIE Specrta of O atom [SO nm SO + O( 3 P,, )] P I(O + ) I(O + ) (arb. Units) P 3 P O ( 4 S o )nd 3 D o 3 P,, VUV, cm - Total kinetic energy release spectrum of O( 3 P ) formed by photodissociation of SO at 93 nm P(E T ) distribution of SO SO(v)+O, E avl =.755eV 93.3nm 3 P P P. P(E) v= v= v= Total KER, ev Ion image of O( 3 P,, )

22 6 5 High-n n (n=34) Rydberg tagging TOF spectrum of O( 3 P ) formed by 93nm photodissociation of SO First single-photon O Rydberg-tagging photon-vuv Rydberg Time-of-flight tagging Spectrum measurement Probe VUV = cm - [p 3 ( 4 S o )nd 3 D o <- 3 P] n = 34 Photolysis l =93.3 nm and.5 nm Total collection time: hour Total Counts nm photodissociation.5 nm photodissociation Time of Flight (μs) Total kinetic energy release spectrum for SO + hυ(93.3 and.5 nm) SO(v) ) + O( 3 P ) High-n Rydberg tagging TOF measurements Rydberg tagging Photolysis at 93.3 nm ν= P(E) (arb. units) Photolysis at.5 nm ν= ν= ν= Ion imaging Total Kinetic energy release (ev)

23 VUV photoionization quadrupole-octopole octopole-quadrupole apparatus Absolute rovibronic state-selected selected cross sections of ion- molecule collisions Product QMS Rf-octopole gas cell Reactant QMS VUV laser Ion detector AB + hν AB(n) + PFI AB + (v +, J + ) + e - Molecular beam Research Team: Ion-molecule reaction dynamics 3

24 Preparation of state-selected selected PFI-photoion or MATI ions for ion-molecule collision studies (a) MATI & Prompt V V Laser 5μs.5V V -6V NO + Ion Signal from MCP Detector (a. u.) MATI Prompt Ion (a) - To Detector V V Time Of Flight (μs) (b) MATI Prompt V V Laser 5μs.7μs.5V V -6V NO + Ion Signal from MCP Detector (a. u.) MATI (b) To Detector V V μs -3V AB + hν AB(n) + PFI AB + (v +, J + ) + e Time Of Flight (μs) H + (v +,N + ) pulsed field ionization (PFI)-photoelectron (PFI-PE) studies (Resolution =4-8 cm - ) 4 H PFI-PE PE (v + =-8) Spectrum hν (cm - ) Peak to 8873 v + = v + =4 v + = (arb. units) I(e-)/I(hν) N + = 3 5 (o) v + =4 hν (cm - ) J" 3 (arb. units) I(e - )/I(hν) v + = v + = v + =3 v + =7 v + =5 v + =6 v + =8 v + =9 v + = v + = v + =3 v + =4 v + =5 v + =6 v + =7 v + = hν (ev) C. Y. Ng, J. Phys. Chem. 3, 5953 (). X4 Potential Energy (ev) hν (ev) 3 + H H + H + v + = 3 v - + = 9 v + = 4 - v + = Interatomic Distance, Å 4

25 Rovibronic state-selected ion-molecule reaction: H + (v +, N + =) + Ne NeH + + H ΔΕ=.5 ev Cross Section (Å ) E lab =. ev E lab =. ev E lab =.6 ev E lab =6.8 ev k(t)=<σv> H + (v +,N + =) + Ne NeH + + H v + H + (v + =-3) + He HeH + + H Compare experimental absolute total cross sections and time- dependent wave packet quantum scattering calculations Cross Section (Å ) v + = v + = 3 v + = Tang et al. LOC Lee et al. QCT Han et al. Han et al. (conv.) Quantum Chu et al., J. Chem. Phys., 443 (5). ( ): Quantum with Coriolis Coupling ( ): Experimental ( ): QCT calculations Collision Energy (ev) 5

26 HD + (v + =-3) + He HeH + (HeD + ) + H Compare expt al cross sections with time-dependent wave packet quantum scattering calculations. Tang et al., J. Chem. Phys. 7, 6438 (7). HeH + Exp. HeD + Exp. HeH + TWQS HeD + TWQS.5 (a) v = (b) v = Cross Section (A )...8 EconvRainer vs HeDv=conv Col 5 vs v_heh Col vs v_hed EHeHv=conv vs HeHv=conv (c) v = (d) v = E T (ev) E T (ev) Ng Group: UC Davis 6

27 ACKNOWLEGMENTS Financial Support: -DOE, AFOSR, NASA -NSF(Chem), NSF(Atm), and NSF(Instrum) Computation Grants - PNNL Computing Facility -NERS Computing Center 7