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Effect of electron correlation on single strand breaks (SSBs) induced by low energy electron (LEE) has been investigated in a fragment excised from a DNA, viz., 2′-deoxycytidine-3′-monophosphate [3′-dCMPH] molecule in gas phase at DFT-B3LYP/6-31+G(d) accuracy level and using local complex potential based time dependent wave packet (LCP-TDWP) approach. The results obtained, in conjunction with our earlier investigation, show the possibility of SSB at very low energy (0.15 eV) where the LEE transfers from π* to σ* resonance state which resembles a SN2 type mechanism. In addition, for the first time, an indication of quantum mechanical tunneling in strand breaking is seen from the highest anionic bound vibrational state (χ5), which may have a substantial role during DNA damage. [ABSTRACT FROM AUTHOR]

Quantum dynamical calculations on HOD subjected to different combinations of IR and UV pulses have been made to isolate field attributes which maximise selectivity and yield in the photodissociation of the desired O-H/O-D bond. Results from IR+UV pulse combinations which provide very high selectivity and/or yield are analysed in detail using population transfer, probability density flow, and flux variations to obtain microdynamic details favouring selectivity and yield. The expectation values for stretch and momentum in O-H and O-D bonds of the H-O-D molecule subjected to UV pulses effecting selective cleavage of these bonds have been analysed to decipher the mechanistic basis of selective dissociation. Fully quantum dynamical calculations using both the ground and excited potential energy surfaces with different initial states and UV pulses reveal that prior stretch in a bond before transferring it to the repulsive first excited state ensures preferential dissociation of this bond. The sampling of large stretch values and a quick downhill motion in the channel corresponding to dissociation of the prestretched bond on the upper surface are seen to underlie this preferential dissociation. [ABSTRACT FROM AUTHOR]

Selective control of HOD photodissociation (H--O + D ← HOD → H + O--D) has been theoretically investigated using CW lasers with appropriate carrier frequency and |0, 0>, |0, 1> and |0, 2> with zero quantum of excitation in the O-H bond and zero, one and two quanta of excitation in the O--D bond as the initial states. Results indicate that the O--H bond in HOD can be selectively dissociated with a maximum flux of 87% in the H + O--D channel from the ground vibrational state |0, 0>. For the O--D bond dissociation, it requires two quanta of excitation (|0, 2>) in the O--D mode to obtain 83% flux in the H--O + D channel. Use of a two colour laser set-up in conjunction with the field optimized initial state (FOIST) scheme to obtain an optimal linear combination of |0, 0> and |0, 1> vibrational states as the initial state provides an additional 7% improvement to flux in the H--O + D channel as compared to that from the pure |0, 1> state. [ABSTRACT FROM AUTHOR]

Abstract: Selective Control of HOD photodissociation has been investigated using simple field profiles. Initial results indicate that preferential dissociation of O–H bond may be achieved from the ground vibrational state and that the O–D bond can be selectively dissociated using only the fundamental excitation in this mode. Dissociation from 2 quanta of excitation in the O–D mode produces 82.8% products with O–D bond dissociation. Preferential maximization of O–D dissociation vis-à-vis O–H bond may also be achieved from the ground vibrational state using a combination of two lasers with carrier frequencies 54920cm−1 and 52203cm−1. The use of Field Optimized Initial STate (FOIST) based scheme to enhance selective control of HOD photodissociation provides additional 6−8% H–O+D products compared to those obtained without FOIST. [Copyright &y& Elsevier]

Abstract: Bond dissociation in the deutereted water molecule HOD has been investigated to explore the possibility of selective control of dissociation of O–H and O–D bonds using simple field profiles and initial states that do not require high overtone excitations. Preliminary results indicate that considerable selectivity in dissociation of O–H and O–D bonds can be achieved using fundamental and first overtone excitations only and use of field optimized initial state (FOIST) based scheme with appropriate choice of field parameters and initial states may enhance both selectivity and yield. [Copyright &y& Elsevier]