either a merged-beam or crossed-beam configuration. In the former, a large number
of ions are excited, while in the latter few are excited, but the window for dissociation is the same for all excited ions. Fragment ions are then identified by scanning
an electrostatic analyser (ESA) and monitoring yields. Action spectra can be
obtained from measurements of photo-induced fragment ion production as a function of wavelength. It is possible to probe the aftermath of interactions between the
ions and a gas and/or an electron captured from an alkali metal. As with all singlepass experiments, fragmentation within a limited window is sampled. Thus the
setup requires fast dissociation on the μs time scale (useful for weakly bond
complexes). Spectra from such an instrument could be skewed to the blue, as ions
0
2
4
6
8
c
m/z
b
a
-NH
2
CH
2
COOH
-NH
3
,-C
2
H
2
O
-H
2
O,-CO
-NH
3
,-H
2
O
-NH
3
110
130
150
170
190
210
0
2
4
6
8
0
2
4
6
8
10
Counts (arb. units)
Fig. 3.14 Photodissociation
mass spectra of [Trp + H]
+
(m/z 205) after (a) 220-nm,
and (b, c) 266-nm
photoexcitation: Fragment
ions were formed (a, b) up to
15 μs and (c) between 57 μs
and 72 μs after
photoexcitation [20]. In the
latter spectrum, dissociation
is of the Trp
+ radical cation
while in the two former
spectra it is of [Trp + H]
+ and
Trp
+ . Trp Tryptophan
34
J.A. Wyer
of ions are excited, while in the latter few are excited, but the window for dissociation is the same for all excited ions. Fragment ions are then identified by scanning
an electrostatic analyser (ESA) and monitoring yields. Action spectra can be
obtained from measurements of photo-induced fragment ion production as a function of wavelength. It is possible to probe the aftermath of interactions between the
ions and a gas and/or an electron captured from an alkali metal. As with all singlepass experiments, fragmentation within a limited window is sampled. Thus the
setup requires fast dissociation on the μs time scale (useful for weakly bond
complexes). Spectra from such an instrument could be skewed to the blue, as ions
0
2
4
6
8
c
m/z
b
a
-NH
2
CH
2
COOH
-NH
3
,-C
2
H
2
O
-H
2
O,-CO
-NH
3
,-H
2
O
-NH
3
110
130
150
170
190
210
0
2
4
6
8
0
2
4
6
8
10
Counts (arb. units)
Fig. 3.14 Photodissociation
mass spectra of [Trp + H]
+
(m/z 205) after (a) 220-nm,
and (b, c) 266-nm
photoexcitation: Fragment
ions were formed (a, b) up to
15 μs and (c) between 57 μs
and 72 μs after
photoexcitation [20]. In the
latter spectrum, dissociation
is of the Trp
+ radical cation
while in the two former
spectra it is of [Trp + H]
+ and
Trp
+ . Trp Tryptophan
34
J.A. Wyer