Post on 18-Dec-2015
transcript
Condensed phase vs. Isolated gas phase spectra
Solution phase
AA
A
A A
AW
W
W
W
W
W W
WWW
WW
W
W
WW
W
W: waterA: sample 12
10
8
6
4
2
0
x10
3
30000295002900028500
Wavenumbers / cm-1
MonomerOrigin
* ** **
****
252
418 252+418
(350.88 nm) (333.33 nm)
Isolated gas phase (Supersonic jet)
AA A
A
AA A
S0
S1
252418
Supersonic expansion technique
Pump
Sample seeded in Helium (~ 2 atm)
V m/s
f (v
) s
/ m
P ~ 1x10-6 torr
Trot ~ 5 KTvib < 50 K
Supersonic expansion
S0
S1
V=0
V=0
V=0
V=0
V=0
V=0
V=0
V=0
Dihedral angles
(i) Conformational isomersSchematic potential energy diagram
(ii) Non-covalently bondedcomplexes
LIF (Laser Induced Fluorescence)
S0,v=0
l1
S1
monitor total fluorescence
Fluorescence excitation spectroscopy
Can we perform spectroscopy in a mass spectrometer?
Yes, we can perform high resolution electronic and vibrational spectroscopy in a mass spectrometer.
How?
Laser Desorption and REMPI (ResonantlyEnhanced MultiphotonIonization)
Time of FlightMass Spectrometry
Supersonic jetexpansion
Ionization source Mass analyzerFormation of non-covalently bonded clusters and high resolution spectroscopy
+ +
Jet-cooled Laser Desorption Time of Flight Mass spectrometer
Home-built Jet-cooled Laser Desorption REMPI (Resonantly Enhanced Multiphoton Ionization)Time OF Flight Mass Spectrometer
Biomolecules (peptides)
Low vaporpressure
Decompose uponheating
Vapor?
Reduce the time-scale for heating
dT/dt = 1011 K/sec
1000 K temp jump in a 10 ns laser pulseDesorption without fragmentation
To bring the molecules in vapor phase
(i) Thermal heating(ii) Laser desorption
Computation: M05-2X, M06-2X, DFT-D level of calculation using Gaussian 09, Gamess programs
Experimental Set up and computational methods
Spectroscopic techniques
S0 v = 0
S1
D0
h1 (UV)tuned
h1 (UV)
1C-R2PI(one color Resonant twophoton ionization)
Mass selectedElectronic spectrum
S0 v = 0
S1
D0
h2 (UV)fixed
h2 (UV)
h1 (IR)tuned
100 ns
RIDIRS(Resonant ion dipInfrared spectroscopy)
IR spectrum
S0 v = 0
S1
D0
h2 (UV)tuned
h2 (UV)
h1 (IR)fixed
100 ns
IR-UV hole-burning spectroscopy
Discriminate different conformers
S0 v = 0
S1
D0
h2 (UV)fixed
h2 (UV)
h1 (UV)tuned
100 ns
UV-UV hole-burning spectroscopy
48040032024016080
Mass (a.m.u.)
Ind
+(I
nd
...H
2O
)+
[In
d...
(H2O
) 2 ]+
(In
d...
Py)
+
(In
d) 2
+ [(In
d) 2
...P
y]+
[(In
d) 2
...P
y...H
2O
]+
(In
d) 3
+
Time of Flight mass spectrum of complexes of indole and pyridine
27.525.022.520.017.515.0Time of Flight (s)
Ind
+
(In
d...
H2O
)+
[In
d...
(H2O
) 2 ]+
(In
d...
Py)
+
(In
d) 2
+ [(
Ind
) 2...
Py]
+
[(In
d) 2
...P
y...H
2O
]+
(In
d) 3
+
Electronic spectra of complexes of indole and pyridine
S0
S1
35240 cm-1
S0
S1
Indole Pyridine
34776 cm-1
S0
S1
34969 cm-1
S0
S1
Indole…pyridinedimer
(Indole)2…pyridinetrimer
35164 cm-1
(35240)
D0D0
D0
D0
h
(349
69)
(351
64)
One-color R2PI spectra
IR spectra of species A and B
36003500340033003200
3526
3411
3309
3269
3281
(a) Exc. at 0-0 band of indole
(b) Exc. at A00
+ 27 cm-1
(c) Exc. at B00
+ 30 cm-1
Wavenumber (cm-1
)
S0 v = 0
S1
D0
h2 (UV)fixed
h2 (UV)
h1 (IR)tuned
100 ns
RIDIRS
Single conformer or multiple conformers of dimer and trimer?
Are all these peaks due totransitions of one or multiple conformers of the trimer?
Are all these peaks due to transitions of one or multiple conformers of the dimer?
IR-UV holeburning spectra of A and B
UV spectrum (IR off)
UV spectrum(IR fixed at 3411 cm-1 band of the trimer)
UV spectrum(IR fixed at 3281 cm-1 band of the trimer)
UV spectrumIR fixed at 3269 cm-1 band of the dimer
S0 v = 0
S1
D0
h2 (UV)tuned
h2 (UV)
h1 (IR)fixed
100 ns
IR-UV holeburningspectroscopy
36003500340033003200
3526
3411
3309
3269
3281
(a) Exc. at 0-0 band of indole
(b) Exc. at A00
+ 27 cm-1
(c) Exc. at B00
+ 30 cm-1
Wavenumber (cm-1
)
Conclusion: One conformer of the dimer and one conformer of the trimer are observed.
Determination of the structures of the observed dimer and trimer
36003500340033003200
(c)
(b)
(a)
(N-H...)(N-H...N)
(Ind)2.Py - 1
(Ind)2.Py - 2
(Ind)2.Py - 3
3269
3309
3411 3281
(N-H...N)
3526
HB3
Wavenumber (cm-1
)
Comparison of experimental and theoretical IR spectra
1.95 Å
(ind)2.py-1
Indole
S0 v = 0
S1
D0
h2 (UV)fixed
h2 (UV)
h1 (IR)tuned
100 ns