absorption of a single photon in agreement with the low energy needed for
dissociation. The width in the internal energy distribution of the ions was, however,
insufficient to account for the decay, and instead it was suggested that the necessity
of two exponential functions to describe the data meant that there are two pathways
300
400
500
600
f
d
b
heme
+
m/z
-CH
2
COOH
-CH
2
COOH
-CH
2
COOH
-His
heme
+ (His)
-CH
2
COOH
c
a
e
350
490
630
770
Fig. 7.14 Mass-analysed Ion Kinetic Energy (MIKE) spectra obtained from collisions
between helium and (a) Fe(III)–heme
+ (m/z 616) or (b) Fe(III)–heme
+ (His) (m/z 771) [31].
Fragmentation spectra acquired at ELISA immediately after photoexcitation with 532-nm light
of (c) Fe(III)–heme
+ or (d) Fe(III)–heme
+ (His), and after storage of the photoexcited ions for
one revolution (e) Fe(III)–heme
+ (100 μs) or (f) Fe(III)–heme
+ (His) (112 μs) [31]. As the
spectra taken at ELISA have low resolution, the MIKE spectra were used to identify fragments
7 Spectroscopy of Ferric Heme and Protoporphyrin IX Ions In Vacuo
131