<span style="font-size:14.0pt;line-height: 115%;font-family:"Times New Roman";mso-fareast-font-family:HiddenHorzOCR; color:black;mso-ansi-language:EN-IN;mso-fareast-language:EN-IN;mso-bidi-language: HI" lang="EN-IN">Competitive energy dynamics in IRMPD of UF₆</span>

49-57The photochemical isotope separation schemes have renewed the detailed investigations of gas phase photophysics and photochemistry of UF6. One of the schemes is based on massive multiphoton excitation of UF6 using one or more suitable IR laser frequency in 16µm region in its ground electronic state. In the present work we have modelled such Infrared Multiphoton Dissociation (IRMPD) on a rate equation formalism. Using RRKM theory, the multiphoton dissociation rate constants for UF6 with 16µm laser have been estimated. It is shown that about 50 laser photons, which are 15 photons excess over the dissociation threshold of 3 eV, are required for dissociation of each UF6 molecule. Using the present model, the fluence dependence of dissociation yield has been evaluated and it is found that MPD of UF6 occurs with a threshold fluence of 1 - 1.2 J cm-2. Isotopic selectivity in this model is described as the difference in the rate of laser energy absorption for the two isotopic species. Considering various time scales involving excitation, collisional deactivation and life time of energized 235- UF6 molecule, the extent of selectivity loss has been estimated

TEA CO<SUB>2</SUB> laser-induced reaction of CH<SUB>3</SUB>NO<SUB>2</SUB> with CF<SUB>2</SUB>HCl: a mechanistic study

Dissociation of nitromethane has been observed when a mixture of CF2HCl and CH3NO2 is irradiated using pulsed TEA CO2 laser at 9R (24) line (1081 cm-1), which is strongly absorbed by CF2HCl but not by CH3NO2. Under low laser fluence conditions, only nitromethane dissociates, whereas at high fluence CF2HCl also undergoes dissociation, showing that dissociation occurs via the vibrational energy transfer processes from the TEA CO2 laser-excited CF2HCl to CH3NO2. Time-resolved infrared fluorescence from vibrationally excited CF2HCl and CH3NO2 molecules as well as UV absorption of CF2 radicals are carried out to elucidate the dynamics of excitation/dissociation and the chemical reactions of the dissociation products

Infrared diode laser probing of methane in excimer laser photolysis of pyruvic acid

The photodissociation of pyruvic acid at 193 nm has been studied and one of the photoproducts, methane, was detected using an infrared diode laser absorption probe technique. Using second-derivative absorption spectroscopy at 1346.326 cm-1[R (-)(7) transition in v4 band], the progress of the reaction was monitored. The quantum yield of formation of methane = 0.09 &#177; 0.01 and was further corroborated by a simple measurement of pressure changes following the photolysis. The secondary photolysis of the photoproduct acetaldehyde via the established route was found to be negligible. This result may help to account for the energetics of the photodissociation process by a 6.4 eV excimer laser photon. The possibility of using this technique to examine the nascent methane molecule in real-time domain to gain better insight of the dissociation dynamics is also indicated

Deciphering the binding modes of hematoporphyrin to bovine serum albumin

175-187Interaction of proteins with small molecules is important in understanding delivery and transport of different therapeutic agents, including drugs. In the present study, we investigated the interaction between hematoporphyrin (HP), the principal component of photosensitizing drug with bovine serum albumin (BSA) in aqueous buffer solution using UV-Vis absorption spectroscopy and fluorescence measurements. The results were further substantiated by molecular docking and molecular dynamics (MD) simulation. Our results revealed that fluorescence of BSA was dominantly quenched by the ground-state complex formation with HP accompanied by the electronic energy transfer (EET) to the later. We experimentally determined the thermodynamic parameters such as G0, H0, and S0 for the HP-BSA system which were -35.5 kJ mole-1,  -56.4 kJ mole-1 and -0.06 kJ mole-1 K-1, respectively. These parameters suggested hydrogen-bonding and Van der Waals forces playing major role in the complexation. This was also supported by the binding energy parameters calculated by molecular docking. Moreover, the experimentally determined G0 nicely correlated with those determined by molecular docking and MD-simulation. Further, computational results clearly showed that the binding of HP with BSA in the subdomains IB and IIA. </span

How Ions Affect the Structure of Water: A Combined Raman Spectroscopy and Multivariate Curve Resolution Study

Raman spectroscopy in combination with multivariate curve resolution (Raman-MCR) is used to explore the interaction between water and various kosmotropic and chaotropic anions. Raman-MCR of aqueous Na-salt (NaI, NaBr, NaNO₃, Na₂SO₄, and Na₃PO₄) solutions provides solute-correlated Raman spectra (SC-spectra) of water. The SC-spectra predominantly bear the vibrational characteristics of water in the hydration shell of anions, because Na⁺-cation has negligible effect on the OH stretch band of water. The SC-spectra for the chaotropic I^–, Br^–, and NO₃^– anions and even for the kosmotropic SO₄^2– anion resemble the Raman spectrum of isotopically diluted water (H₂O/D₂O = 1/19; v/v) whose OH stretch band is largely comprised by the response of vibrationally decoupled OH oscillators. On the other hand, the SC-spectrum for the kosmotropic PO₄^3– anion is quite similar to the Raman spectrum of H₂O (bulk). Comparison of the peak positions of SC-spectra and the Raman spectrum of isotopically diluted water suggests that the hydrogen bond strength of water in the hydration shell of SO₄^2– is comparable to that of the isotopically diluted water, but that in the hydration shell of I^–, Br^–, and NO₃^– anions is weaker than that of the latter. Analysis of integrated area of component bands of the SC-spectra reveals ∼80% reduction of the delocalization of vibrational modes (intermolecular coupling and Fermi resonance) of water in the hydration shell of I^–, Br^–, NO₃^–, and SO₄^2– anions. In the case of trivalent PO₄^3–, the vibrational delocalization is presumably reduced and the corresponding decrease in spectral response at ∼3250 cm^–1 is compensated by the increased signal of strongly hydrogen bonded (but decoupled) water species in the hydration shell. The peak area-averaged wavenumber of the SC-spectrum increases as PO₄^3– < SO₄^2– < NO₃^– < Br^– < I^– and indeed suggests strong hydrogen bonding of water in the hydration shell of PO₄^3– anion