266 nm photolysis of CF3I and C2F5I studied by diode laser gain FM spectroscopy

Hancock, Gus; Hutchinson, Albert L.; Peverall, R.; Richmond, Graham; Ritchie, Grant A. D.; Taylor, Sarah

doi:10.1039/b617414k

Cited by 11 publications

(27 citation statements)

References 41 publications

(55 reference statements)

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“…The detected signals were amplified using either one, or two, 500 MHz amplifiers (Minicircuits ZFL-500LN) as required, and then demodulated with reference to the rf signal applied to the EOM in an rf demodulator circuit (Pulsar Microwave). The resulting The nascent pure FM absorption profiles were extracted by the method used in our previous work [45]. …”

Section: Methodsmentioning

confidence: 99%

Frequency modulated circular dichroism spectroscopy: application to ICN photolysis

et al. 2010

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Section: Methodsmentioning

confidence: 99%

Frequency modulated circular dichroism spectroscopy: application to ICN photolysis

et al. 2010

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“…11,17 A glass tube containing molecular iodine (Aldrich, 499% purity), heated to approximately 10 1C above room temperature in order to increase the vapour pressure, was connected to a 1.5 m glass photolysis cell via Teflon tubing. 11,17 A glass tube containing molecular iodine (Aldrich, 499% purity), heated to approximately 10 1C above room temperature in order to increase the vapour pressure, was connected to a 1.5 m glass photolysis cell via Teflon tubing.…”

Section: Experimental and Analysismentioning

confidence: 99%

“…11,17 First, a numerical integration over a series of time intervals with limits separated by 100 ns of the recorded I and Q signals was performed. 11,17 First, a numerical integration over a series of time intervals with limits separated by 100 ns of the recorded I and Q signals was performed.…”

Section: Experimental and Analysismentioning

confidence: 99%

“…The overall setup for the time-resolved FM experiment is similar to that employed in our previous work. 11,17 A glass tube containing molecular iodine (Aldrich, 499% purity), heated to approximately 10 1C above room temperature in order to increase the vapour pressure, was connected to a 1.5 m glass photolysis cell via Teflon tubing. This arrangement generated a constant low pressure flow of B30 mTorr of I 2 through the cell.…”

Section: Experimental and Analysismentioning

confidence: 99%

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Diode laser based studies of the UV photolysis of molecular iodine

Hancock

Richmond

Ritchie

et al. 2009

Phys. Chem. Chem. Phys.

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The photolysis of molecular iodine at 193 and 248 nm has been studied by diode laser based frequency-modulated (FM) absorption spectroscopy with detection of the nascent iodine photofragment via the I((2)P(1/2)-(2)P(3/2)) transition at 1.315 microm. Use of narrow band radiation enables nascent measurements with sufficient speed resolution to allow both the character of the initial electronic transition and speed of the fragments to be determined. The time dependence of the integrated area of the measured Doppler profiles has been used to determine both the I* quantum yield and the collisional electronic quenching rate constant of I* (I* = (2)P(1/2)) by I(2). These values are also determined using the diode laser gain versus absorption technique. In the 248 nm case an I* quantum yield of 0.45 +/- 0.04 and 0.42 +/- 0.04 is found by each method, respectively, and an electronic quenching rate constant of (3.6 +/- 0.5) x 10(-11) cm(3) molecule(-1) s(-1), consistent with literature, is determined. The form of the nascent Doppler profile indicates that excitation to a Omega = 1 state dominates, with subsequent dissociation to I((2)P(1/2)) + I((2)P(3/2)), in keeping with assignment of the upper state as 1441 (3)Sigma(+)(1(u)). The deviation from Phi(I*) = 0.5 can be attributed to a contribution from the 1441 (3)Sigma(+)(0(u)(-)) state which dissociates to two ground state iodine atoms. 193 nm excitation exhibits more complicated dynamics and kinetics, including a pressure dependent I* quantum yield. At the low pressures, <200 mTorr, used in the FM Doppler measurements there are two speed components to the profile suggesting multiple dissociation pathways. Firstly, fast iodine fragments indicate single photon absorption in a parallel transition followed by direct dissociation. Secondly, a slower speed component can be attributed to iodine atoms formed after radiative transfer to unbound levels in the ground state and the a' surface. Investigation of the changes in Doppler profiles with time suggest that some of the a' surface population may transfer to the bound B((3)Pi(0u)(+)) state which then in turn undergoes collision-induced predissociation to produce I atoms on the ground electronic state.

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“…A prime example in this category is the CF 3 I molecule, which has 18 more valence electrons than un-substituted methyl iodide. It has been the subject of numerous experiments in which I* quantum yields have been obtained [5][6][7][8][9][10][11][12][13][14][15][16][17][18] and its absorption spectrum has also been measured. [19][20][21][22] Theoretical studies of CF 3 I are much rarer, but ab initio calculations have also been reported for this system, 23,24 as well as a treatment of its photodissociation dynamics.…”

Section: Introductionmentioning

confidence: 99%

Potential energy surfaces for ground and excited electronic states of the CF3I molecule and their relevance to its A-band photodissociation

Alekseyev

Liebermann

Buenker

2013

Phys. Chem. Chem. Phys.

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The multireference spin-orbit (SO) configuration interaction (CI) method in its Λ-S contracted SO-CI version is employed to calculate two-dimensional potential energy surfaces for the ground and low-lying excited states of CF3I relevant to its photodissociation in the lowest absorption band (A band). The computed equilibrium geometry for the X̃A1 ground state and vibrational frequency ν3 for the C-I stretch mode agree well with available experimental data. The (3)Q0(+) state dissociating to the excited I((2)P1/2) limit is found to have a minimum of 1570 cm(-1) significantly shifted to larger internuclear distances (RC-I = 5.3 a0) relative to the ground state. Similar to the CH3I case, this makes a single-exponent approximation commonly employed for analysis of the CF3I recoil dynamics unsuitable. The 4E((3)A1) state possessing an allowed transition from the ground state and converging to the same atomic limit as (3)Q0(+) is calculated to lie too high in the Franck-Condon region to have any significant impact on the A-band absorption. The computed vertical excitation energies for the (3)Q1, (3)Q0(+), and (1)Q states indicate that the A-band spectrum must lie approximately between 31,300 and 45,200 cm(-1), i.e., between 220 and 320 nm. This result is in very good agreement with the measured absorption spectrum.

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266 nm photolysis of CF3I and C2F5I studied by diode laser gain FM spectroscopy

Cited by 11 publications

References 41 publications

Frequency modulated circular dichroism spectroscopy: application to ICN photolysis

Frequency modulated circular dichroism spectroscopy: application to ICN photolysis

Diode laser based studies of the UV photolysis of molecular iodine

Potential energy surfaces for ground and excited electronic states of the CF3I molecule and their relevance to its A-band photodissociation

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