194
R. Fausto and N. Kuş
near-IR light emitted by a Quanta-Ray moPo-SL pulsed optical parametric oscillator at different wavelengths, corresponding to the overtone absorptions of the two
amino-hydroxy forms. upon irradiation at 7,013 cm
−1
, the initially most populated
Ah1 conformer converted into Ah2, whereas upon irradiation at 7,034 cm
−1
the
reversed reaction was observed. the changes were monitored by observation of the
mid-IR spectra of the irradiated matrix (Fig. 7.17) [78].
use of narrowband selective near-IR irradiation of matrix-isolated small
molecules, in particular small carboxylic acids, to induce conformational changes
had already been successful [79–81]. however, before the study on cytosine, these
phenomena had never been reported for larger heterocyclic molecules. In polyatomic
molecules containing more than ten atoms, the higher density of vibrational states
may affect the pathways of vibrational energy redistribution and, hence, the
efficiency of rotational isomerization stimulated by excitation of the overtones of
stretching vibrations. In this regard, the study on cytosine [78] has also constituted
a noteworthy experimental achievement.
N
N
N
H
H
O
H
N
N
N
H
H
O
H
N
N
N
H
H
O
H
N
N
N
H
O
H
H
N
N
N
H
O
H
H
AO
AH1
A H2
IO1
I O2
Fig. 7.16 Lowest energy isomeric forms of cytosine
R. Fausto and N. Kuş
near-IR light emitted by a Quanta-Ray moPo-SL pulsed optical parametric oscillator at different wavelengths, corresponding to the overtone absorptions of the two
amino-hydroxy forms. upon irradiation at 7,013 cm
−1
, the initially most populated
Ah1 conformer converted into Ah2, whereas upon irradiation at 7,034 cm
−1
the
reversed reaction was observed. the changes were monitored by observation of the
mid-IR spectra of the irradiated matrix (Fig. 7.17) [78].
use of narrowband selective near-IR irradiation of matrix-isolated small
molecules, in particular small carboxylic acids, to induce conformational changes
had already been successful [79–81]. however, before the study on cytosine, these
phenomena had never been reported for larger heterocyclic molecules. In polyatomic
molecules containing more than ten atoms, the higher density of vibrational states
may affect the pathways of vibrational energy redistribution and, hence, the
efficiency of rotational isomerization stimulated by excitation of the overtones of
stretching vibrations. In this regard, the study on cytosine [78] has also constituted
a noteworthy experimental achievement.
N
N
N
H
H
O
H
N
N
N
H
H
O
H
N
N
N
H
H
O
H
N
N
N
H
O
H
H
N
N
N
H
O
H
H
AO
AH1
A H2
IO1
I O2
Fig. 7.16 Lowest energy isomeric forms of cytosine