原子分子光谱学
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What we have known • S1 ← S0 at ~ 294 nm (4.19 eV), IE = 7.720 eV • theoretic prediction: (a) S1 ← S0 ~ ring, (b) ionization ~
the removal of an electron from the amino part (experimental evidence is not yet available) • cation data of deuterated species are not yet available
Chapter 10. REMPI, ZEKE, and MATI Spectroscopies 10.1 REMPI spectroscopy Resonance-enhanced multiphoton ionization (REMPI) spectroscopy involves more than one photons in the ionization process. In general, the REMPI process occurs by a resonant mphoton excitation from a ground electronic state to an excited (ro)vibronic state. from a ground electronic state to an excited state and n photons from the neutral excited state to and ionic state. More (n) additional photons are then absorbed and the molecule is ionized. The probability of ionization is enhanced by the fact that the first m photons are resonant with an intermediate state.
34200
34400
34600
34800
35000
35200
One photon energy / cm-1
wbt 10
1C-R2PI spectra of deuterium substituted aniline isotopomers
(a) 000
6a0
-1 1
34193 cm
I0
2
120
1
wbt 12
(1) a molecule (M) is prepared in S0 state by molecular beam methods. (2) M is excited by the first laser to a particular vibrational level in the electronically excited S1 state (M*). (3) M* is excited by the second laser to a high-n (n > 150) Rydberg state (M**). (4) M** is ionized by PFI, and ZEKE electrons and ZEKE ions are generated simultaneously. (5) ZEKE photoelectron spectroscopy detects the ZEKE electrons.
Approaches • preparation of C6H5NH2, C6H5NHD, C6H5ND2, C6D5NH2, C6D5NHD, C6D5ND2 • 1C-R2PI and MATI experiments Goals • EE, IE, vibrations in the S1 and D0 states • D-substitution effect on transition energy and vibration • site-specific electronic transition
wbt 14
MATI spectra of deuterium substituted aniline isotopomers
(a) C6D5NH2
Relative Intensity
(b) 000
34195 cm
-1
6a0
1
1Baidu Nhomakorabea0 I0
2
1
(b) C6D5NHD
0 (c) 00
34202 cm
-1
6a0
1
I0
2
(c) C6D5ND2
120
1
0
200
400
600
800
1000
wbt
Relative Wavenumber / cm-1
Most commonly used is resonance-enhanced two-photon ionization, termed (1+1’) R2PI.
wbt 1
wbt
2
The great advantages of the REMPI technique, compared to other approaches such as laser-induced fluorescence (LIF) are its (1) mass selectivity and (2) its state selectivity.
C6H5NH2, S0
wbt 6
Preparation of C6H5NHD and C6H5ND2
H H H H N H H H
H H H H H
+
D2O
H
N D
(Mass 93)
(Mass 94)
H H D H N D H H
(Mass 95)
wbt
7
Preparation of C6H5NHD and C6H5ND2
IAMS, Academia Sinica, Taiwan, 台灣 中研院原分所 wbt 5
Energy Level of Aniline
C6H5NH2 , D0 IE = 62,271 cm (7.7206 eV) C6H5NH2 , S1
* -1 +
E = 34,029 cm
-1
(293.87 nm)
wbt
3
1C and 2C-REMPI spectra of phenol•N2
E2 = 31521 cm-1
Ref.: K. Mü llerDethlefs, J. Chem. Phys. 109, 9244 (1998).
wbt
4
MATI spectroscopy of aniline isotopomers
wbt
13
10.3 MATI spectroscopy
Mass analyzed threshold ionization (MATI) spectroscopy was developed in 1991 by P. Johnson. This method involves detection of ZEKE ions. One of the major advantages of MATI over ZEKE is that it provides mass information. Thus, MATI spectroscopy is suitable for spectroscopic and dynamics studies of isotopomers, radicals, clusters, etc. In the MATI experiments, the prompt ions, ZEKE electrons, and Rydberg neutrals are formed simultaneously. About 50 ns after the occurrence of the laser pulses, (ZEKE electrons are gone) a pulsed electric field of -1.0 V/cm is switched on to reject the prompt ions. After about 8-10 microsecond later, a second pulsed electric field of +400 V/cm is applied to field-ionize the Rydberg neutrals. These threshold (MATI) ions are then accelerated and detected by an ion detector.
Relative Intensity
(b)
98 99
λ = 292.54 nm 98 ↔ C6D5NH2+ 99 ↔ C6D5NHD+
(c)
100
λ = 292.48 nm 100 ↔ C6D5ND2+
92
96
100
104
108
wbt
Mass / amu
9
1C-R2PI spectra of deuterium substituted aniline isotopomers
(a)
00
0 -1
6a0
1
10 I0
2
1
34029 cm
120
1
(a) C6H5NH2
Relative Intensity
(b)
00
0 -1
34031 cm
6a0
1
120 I0
2
1
(b) C6H5NHD
10
1
(c)
00 -1 34038 cm
0
6a0
1
I0
2
120 10
1
1
(b) C6H5ND2
34000
11
10.2 ZEKE spectroscopy Recall that, in photoelectron spectroscopy (PES) a high-energy photon ionizes a molecule and the kinetic energy of the resulting photoelectron is analyzed to reveal the energy levels of the corresponding ion. A typical resolution of PES is 10 meV (80 cm-1). Threshold photoelectron spectroscopy (TPES) is an improved version of PES. It detects electrons emitted only at the threshold of a specific ionic eigenstate. Zero-kinetic energy (ZEKE) photoelectron spectroscopy was developed in 1984 by K. Mü ller-Dethlefs and E.W. Schlag. In this scheme, the system (molecule) is photoexcited to a high-n (n > 150) Rydberg state, and then after a time delay of several microseconds, ionization of the Rydberg neutral is induced by a pulsed electric field. The process is often referred to as ZEKEpulsed field ionization (PFI). The best resolution of ZEKE spectroscopy is 0.15 cm-1, whereas a typical resolution is 3–5 cm-1.
H H H H N H H H
H H H H H
+
D2O
H
N D
(Mass 93)
(Mass 94)
H H D H N D H H
(Mass 95)
wbt
8
TOF spectra of deuterium substituted aniline isotopomers
(a)
94 93
λ = 293.94 nm 93 ↔ C6H5NH2+ 94 ↔ C6H5NHD+
the removal of an electron from the amino part (experimental evidence is not yet available) • cation data of deuterated species are not yet available
Chapter 10. REMPI, ZEKE, and MATI Spectroscopies 10.1 REMPI spectroscopy Resonance-enhanced multiphoton ionization (REMPI) spectroscopy involves more than one photons in the ionization process. In general, the REMPI process occurs by a resonant mphoton excitation from a ground electronic state to an excited (ro)vibronic state. from a ground electronic state to an excited state and n photons from the neutral excited state to and ionic state. More (n) additional photons are then absorbed and the molecule is ionized. The probability of ionization is enhanced by the fact that the first m photons are resonant with an intermediate state.
34200
34400
34600
34800
35000
35200
One photon energy / cm-1
wbt 10
1C-R2PI spectra of deuterium substituted aniline isotopomers
(a) 000
6a0
-1 1
34193 cm
I0
2
120
1
wbt 12
(1) a molecule (M) is prepared in S0 state by molecular beam methods. (2) M is excited by the first laser to a particular vibrational level in the electronically excited S1 state (M*). (3) M* is excited by the second laser to a high-n (n > 150) Rydberg state (M**). (4) M** is ionized by PFI, and ZEKE electrons and ZEKE ions are generated simultaneously. (5) ZEKE photoelectron spectroscopy detects the ZEKE electrons.
Approaches • preparation of C6H5NH2, C6H5NHD, C6H5ND2, C6D5NH2, C6D5NHD, C6D5ND2 • 1C-R2PI and MATI experiments Goals • EE, IE, vibrations in the S1 and D0 states • D-substitution effect on transition energy and vibration • site-specific electronic transition
wbt 14
MATI spectra of deuterium substituted aniline isotopomers
(a) C6D5NH2
Relative Intensity
(b) 000
34195 cm
-1
6a0
1
1Baidu Nhomakorabea0 I0
2
1
(b) C6D5NHD
0 (c) 00
34202 cm
-1
6a0
1
I0
2
(c) C6D5ND2
120
1
0
200
400
600
800
1000
wbt
Relative Wavenumber / cm-1
Most commonly used is resonance-enhanced two-photon ionization, termed (1+1’) R2PI.
wbt 1
wbt
2
The great advantages of the REMPI technique, compared to other approaches such as laser-induced fluorescence (LIF) are its (1) mass selectivity and (2) its state selectivity.
C6H5NH2, S0
wbt 6
Preparation of C6H5NHD and C6H5ND2
H H H H N H H H
H H H H H
+
D2O
H
N D
(Mass 93)
(Mass 94)
H H D H N D H H
(Mass 95)
wbt
7
Preparation of C6H5NHD and C6H5ND2
IAMS, Academia Sinica, Taiwan, 台灣 中研院原分所 wbt 5
Energy Level of Aniline
C6H5NH2 , D0 IE = 62,271 cm (7.7206 eV) C6H5NH2 , S1
* -1 +
E = 34,029 cm
-1
(293.87 nm)
wbt
3
1C and 2C-REMPI spectra of phenol•N2
E2 = 31521 cm-1
Ref.: K. Mü llerDethlefs, J. Chem. Phys. 109, 9244 (1998).
wbt
4
MATI spectroscopy of aniline isotopomers
wbt
13
10.3 MATI spectroscopy
Mass analyzed threshold ionization (MATI) spectroscopy was developed in 1991 by P. Johnson. This method involves detection of ZEKE ions. One of the major advantages of MATI over ZEKE is that it provides mass information. Thus, MATI spectroscopy is suitable for spectroscopic and dynamics studies of isotopomers, radicals, clusters, etc. In the MATI experiments, the prompt ions, ZEKE electrons, and Rydberg neutrals are formed simultaneously. About 50 ns after the occurrence of the laser pulses, (ZEKE electrons are gone) a pulsed electric field of -1.0 V/cm is switched on to reject the prompt ions. After about 8-10 microsecond later, a second pulsed electric field of +400 V/cm is applied to field-ionize the Rydberg neutrals. These threshold (MATI) ions are then accelerated and detected by an ion detector.
Relative Intensity
(b)
98 99
λ = 292.54 nm 98 ↔ C6D5NH2+ 99 ↔ C6D5NHD+
(c)
100
λ = 292.48 nm 100 ↔ C6D5ND2+
92
96
100
104
108
wbt
Mass / amu
9
1C-R2PI spectra of deuterium substituted aniline isotopomers
(a)
00
0 -1
6a0
1
10 I0
2
1
34029 cm
120
1
(a) C6H5NH2
Relative Intensity
(b)
00
0 -1
34031 cm
6a0
1
120 I0
2
1
(b) C6H5NHD
10
1
(c)
00 -1 34038 cm
0
6a0
1
I0
2
120 10
1
1
(b) C6H5ND2
34000
11
10.2 ZEKE spectroscopy Recall that, in photoelectron spectroscopy (PES) a high-energy photon ionizes a molecule and the kinetic energy of the resulting photoelectron is analyzed to reveal the energy levels of the corresponding ion. A typical resolution of PES is 10 meV (80 cm-1). Threshold photoelectron spectroscopy (TPES) is an improved version of PES. It detects electrons emitted only at the threshold of a specific ionic eigenstate. Zero-kinetic energy (ZEKE) photoelectron spectroscopy was developed in 1984 by K. Mü ller-Dethlefs and E.W. Schlag. In this scheme, the system (molecule) is photoexcited to a high-n (n > 150) Rydberg state, and then after a time delay of several microseconds, ionization of the Rydberg neutral is induced by a pulsed electric field. The process is often referred to as ZEKEpulsed field ionization (PFI). The best resolution of ZEKE spectroscopy is 0.15 cm-1, whereas a typical resolution is 3–5 cm-1.
H H H H N H H H
H H H H H
+
D2O
H
N D
(Mass 93)
(Mass 94)
H H D H N D H H
(Mass 95)
wbt
8
TOF spectra of deuterium substituted aniline isotopomers
(a)
94 93
λ = 293.94 nm 93 ↔ C6H5NH2+ 94 ↔ C6H5NHD+