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CHEM01200604005 A. K. Pathak - Homi Bhabha National Institute

CHEM01200604005 A. K. Pathak - Homi Bhabha National Institute

CHEM01200604005 A. K. Pathak - Homi Bhabha National Institute

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figure that the FT-DACF IR spectrum is far off from the experimental spectrum. 24 It is<br />

worthwhile to mention that for this open shell system, IR spectra generated applying FT<br />

of velocity autocorrelation function (FT-VACF) has a poorer match than that by FT-<br />

DACF procedure.<br />

Cl 2 .- .H 2<br />

O<br />

Cl 2 .- .2H 2<br />

O (II-B)<br />

IR Intensity<br />

IR Intensity<br />

3000 3200 3400 3600 3800<br />

Frequency (cm -1 )<br />

3000 3200 3400 3600 3800<br />

Frequency (cm -1 )<br />

A<br />

B<br />

Fig. 3.3. Calculated scaled IR spectra at BHHLYP/6-311++G(d,p) level for (A) Cl 2•¯.H 2 O and (B)<br />

Cl 2•¯.2H 2 O. The scaling factor is taken as 0.92 to account for the anharmonic nature of stretching<br />

vibrations. Lorentzian line shape has been applied with peak half-width of 20 cm -1 .<br />

For Cl •− 2 .3H 2 O, Cl •− 2 .4H 2 O and Cl •− 2 .5H 2 O clusters, 10, 15 and 24 minimum<br />

energy structures have been found at BHHLYP/6-311++G(d,p) level, respectively. The<br />

structures which have population of >1% are considered (displayed in Fig. 3.2) and their<br />

population is shown in Table 3. 1. Frequency is also calculated by taking the anharmonic<br />

nature of vibration using vibrational self-consistent field (VSCF) method. As the VSCF<br />

calculation is found to be very costly method for this open shell system, an appropriate<br />

scaling is carried out of the normal mode to include the anharmonic nature of vibrations.<br />

Based on the anhamonic calculation, it is also found that different modes have different<br />

anharmonicity. So different scaling is carried out in the regions having energy range of<br />

64

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