Quantum yield of Cl<SUP>&#8727;</SUP> (<SUP>2</SUP>P<SUB>&#189;</SUB>) production in the gas phase photolysis of CCl<SUB>4</SUB> in the ultraviolet

In this paper, we have probed the dynamics of chlorine atom production from the gas phase photodissociation of carbon tetrachloride at 222 and 235 nm. The quantum yield, &#966;&#8727; of Cl&#8727; (2P&#189;) production has been determined by probing the nascent concentrations of both excited (2P&#189;) and ground state (2P3/2) chlorine atoms by suitable resonance-enhanced multiphoton ionization (REMPI) detection schemes. Although at the photolysis wavelengths the absorption of carbon tetrachloride is weak, significant amounts of Cl&#8727; are produced. Surprisingly, the quantum yield of Cl&#8727; production does not follow the absorption spectrum closely, which gives rise to the possibility of an indirect dissociation mechanism present in CCl4 along with direct dissociation at these ultraviolet wavelengths

Metal-assisted red light-induced efficient DNA cleavage by dipyridoquinoxaline-copper(II) complex

Complete cleavage of double stranded pUC19 DNA by the complex [Cu(dpq)2(H2O)](ClO4)2 (dpq, dipyridoquinoxaline) has been observed on irradiation at 694 nm from a pulsed ruby laser, assisted by the metal d-band transition as well as the quinoxaline triplet states in the absence of any external additives

Photodissociation of o-C<SUB>6</SUB>H<SUB>4</SUB>I(CH<SUB>2</SUB>Cl) in the near ultraviolet: a case of photoselective C-I bond dissociation

We report the photodissociation dynamics of ortho-iodobenzyl chloride (o-C6H4I(CH2Cl)) in the ultraviolet. The gas phase dissociation dynamics of o-iodobenzyl chloride at 222, 236, 266, 280, and ~304 nm was monitored by probing the quantum yields of I&#8727; (2P&#189;) as well as Cl&#8727; (2P&#189;) production using suitable resonance enhanced multiphoton ionization detection schemes. We find that only iodine atoms in the ground (I (2P3/2)) as well as excited (I&#8727;) states are produced in the dissociation. No Cl (2P3/2) or Cl&#8727; atoms were detected. This accidental bond selective dissociation in o-iodobenzyl chloride is perhaps due to weak coupling among various chromophores present in the molecule and inefficient interchromophore energy transfer among them

Photodissociation of o−C6H4I(CH2Cl)o-C_6H_4I(CH_2Cl) in the near ultraviolet: a case of photoselective C-I bond dissociation

We report the photodissociation dynamics of ortho-iodobenzyl chloride $(o-C_6H_4I(CH_2Cl))$ in the ultraviolet. The gas phase dissociation dynamics of o-iodobenzyl chloride at 222, 236, 266, 280, and $\sim304 nm$ was monitored by probing the quantum yields of $I^* \hspace {2mm} (^2P_{1/2})$ as well as $Cl^* \hspace {2mm}(^2P_{1/2})$ production using suitable resonance enhanced multiphoton ionization detection schemes. We find that only iodine atoms in the ground $(I (^2P_{3/2}))$ as well as excited $(I^*)$ states are produced in the dissociation. No $Cl (^2P_{3/2})$ or $Cl^*$ atoms were detected. This accidental bond selective dissociation in o-iodobenzyl chloride is perhaps due to weak coupling among various chromophores present in the molecule and inefficient interchromophore energy transfer among them

Cl∗(<SUP>2</SUP>P<SUB>½</SUB>) production dynamics from chloroiodomethane (CH<SUB>2</SUB>ICl) in the ultraviolet

Dynamics of Cl∗(<SUP>2</SUP>P<SUB>½</SUB>) production from chloroiodomethane dissociation has been investigated in the near ultraviolet (222≤λ<SUB>ex</SUB>≤304 nm). The quantum yield of Cl∗((<SUP>2</SUP>P<SUB>½</SUB>) production, φ∗(Cl), has been measured by monitoring nascent Cl(<SUP>2</SUP>P<SUB>3/2</SUB>) and Cl∗ concentrations and compared with the quantum yield of I∗(<SUP>2</SUP>P<SUB>½</SUB>) production at the same excitation wavelengths. In the near ultraviolet where most of the transition strength is carried by the σ∗(C-I)← n(I) transition, the measured Cl½ quantum yield decreases as a function of increasing photolysis wavelength. An interchromophore energy transfer mechanism between the C-I and C-Cl chromophores has been proposed to rationalize Cl∗ production since the direct excitation of the σ∗(C-I)← n(Cl) transition is less likely at wavelengths ~100 nm away from the peak of the C-Cl absorption band

Pulsed laser degradation of polyethylene oxide and polyacrylamide in aqueous solution.

The kinetics of degradation of polyethylene oxide (PEO) and polyacrylamide (PAM) was investigated using a pulsed Nd:YAG laser, operating at 266 nm wavelength with $\sim 6$ ns pulses. Gel permeation chromatograph was used to monitor the change in molecular weight with time. Continuous distribution kinetics for random chain scission was used to obtain the rate coefficient for the degradation process. The measured rate coefficients for the degradation are $1.9\times 10^4$ and $1.2\times 10^4 \hspace {5mm} s^{-1}$ for PEO and PAM, respectively. A pathway for degradation has been proposed based on the experimental observations. The signi.cance of polymer concentration and the laser light intensity along with the requirement of oxygen for degradation has been correlated to the mechanism of the degradation process. The degradation was found to decrease with increasing polymer concentration while a threshold light intensity was required to initiate the degradation process

Photodissociation dynamics of CH2ICl at 222, 236, 266, 280, and-304 nm

Dynamics of I*(P-2(1/2)) formation from CH2ICl dissociation has-been investigated at five different ultraviolet excitation wavelengths, e.g., 222, 236, 266, 280, and similar to304 nm. The quantum yield of I*((2)p(1/2)) production, phi*, has been measured by monitoring nascent I(P-2(3/2)) and I* concentrations using a resonance enhanced multiphoton ionization detection scheme. The measured quantum yield as a function of excitation energy follows the same trend as that of methyl iodide except at 236 run. The photodissociation dynamics of CH2ICl also involves three upper states similar to methyl iodide, and a qualitative correlation diagram has been constructed to account for the observed quantum yield. From the difference in behavior at 236 nm, it appears that the crossing region between the two excited states ((3)Q(0) and (1)Q(1)) is located near the exit valley away from the Franck Condon excitation region. The B- and C-band transitions do not participate in the dynamics, and the perturbation of the methyl iodide states due to Cl-I interaction is relatively weak at the photolysis wavelengths employed in this investigation

Quantum yield of Cl* (2P1/2) production in the gas phase photolysis of CCl4 in the ultraviolet

In this paper, we have probed the dynamics of chlorine atom production from the gas phase photodissociation of carbon tetrachloride at 222 and 235 nm. The quantum yield, phi* of Cl* (P-2(1/2)) production has been determined by probing the nascent concentrations of both excited (P-2(1/2)) and ground state (P-2(3/2)) chlorine atoms by suitable resonance-enhanced multiphoton ionization (REMPI) detection schemes. Although at the photolysis wavelengths the absorption of carbon tetrachloride is weak, significant amounts of Cl* are produced. Surprisingly, the quantum yield of Cl* production does not follow the absorption spectrum closely, which gives rise to the possibility of an indirect dissociation mechanism present in CCl4 along with direct dissociation at these ultraviolet wavelengths