- Email: [email protected]
2) in collisions with N2 molecules and rare gas atoms
Chemical Physics Letters 406 (2005) 259–262 www.elsevier.com/locate/cplett
Laser-induced fluorescence study of the quenching of Cl(2P1/2) in collisions with N2 molecules and rare gas atoms Fumikazu Taketani, Aya Yamasaki, Kenshi Takahashi, Yutaka Matsumi
*
Solar–Terrestrial Environment Laboratory and Graduate School of Science, Nagoya University, 3-13 Honohara, Toyokawa, Aichi 442-8507, Japan Received 30 January 2005; in final form 3 March 2005 Available online 23 March 2005
Abstract The rate constants of physical quenching of Cl(2P1/2) in collisions with N2 molecules and rare gas atoms (Rg = He, Ne and Ar) at 295 ± 2 K were investigated using a technique of vacuum ultraviolet laser-induced fluorescence spectroscopy. The rate constants determined are (7.6 ± 0.8) · 1015, (5.7 ± 0.3) · 1014, 68 · 1016 and 65 · 1016 cm3 molecule1 s1 for collision partners of N2, He, Ne and Ar, respectively. 2005 Elsevier B.V. All rights reserved.
1. Introduction The spin–orbit states of Cl(2P3/2) (denoted Cl) and Cl(2P1/2) (denoted Cl*) are separated in energy by 882 cm1, with the Cl* being higher in energy. The relaxation processes of Cl* in collisions with small molecules and rare gas atoms have been studied with a variety of experimental techniques such as atomic resonance absorption spectroscopy in the VUV (ARA-VUV) [1–3], atomic resonance absorption spectroscopy in the IR region (ARA-IR) [4], laser magnetic resonance (LMR) [5–7] and resonance fluorescence spectroscopy with an atomic resonance lamp (RF) [8]. Quantum chemical calculations have also been performed to investigate the potential energy curves for the lowest adiabatic states X2R and A2P of Cl–Rg complexes and to estimate the quenching cross-sections of Cl* in collisions with rare gas atoms (Rg) [9]. The rate constants reported previously are summarized in Table 1. In this work, the vacuum ultraviolet laser-induced fluorescence spectroscopy (VUV-LIF) have been applied to the experimental studies to determine the rate con*
Corresponding author. Fax: +81 533 89 5593. E-mail address: [email protected] (Y. Matsumi).
0009-2614/$ - see front matter 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.cplett.2005.03.003
stants of the physical quenching of Cl* atom in collisions with N2 molecules and rare gas atoms (Rg = He, Ne and Ar) at 295 ± 2 K. HCl molecules in the presence of excess N2 or Rg were irradiated with the 193 nm laser light. The temporal decay profiles of the Cl* atom produced from HCl photolysis were detected by the VUVLIF technique at 135.17 nm. The room temperature rate constants determined are compared with the available literature values.
2. Experimental section The experimental setup used in this work is essentially the same as in our previous studies on the photochemical reaction processes of Cl* and Cl [10–12]. Therefore, only a brief description related to this work will be given here. All the experiments were performed at 295 ± 2 K. The gas mixtures of a small amount of HCl and an excess of N2 or Rg were slowly introduced into the chamber through mass flow controllers. The total pressure in the cell was measured by a capacitance manometer (MKS, Baratron 622A). The reaction chamber was evacuated continuously by a rotary pump through a liquid N2 trap. The gas mixtures were irradiated
F. Taketani et al. / Chemical Physics Letters 406 (2005) 259–262
Table 1 Rate constants of the physical quenching processes of Cl* in collisions with N2 and rare gas atoms (He, Ne and Ar) at room temperature Collision partner
ka
Techniqueb
Reference
N2
6.3 ± 1.0(13) 4.0 ± 1.0(13) 3.9 ± 1.5(14) 5.0 ± 1.5(15) 7.6 ± 0.8(15)
ARA-VUV ARA-IR LMR RF VUV-LIF
[3] [4] [7] [8] This work
He
3.8 ± 0.6(15) 7.3 ± 2.0(14) 6.0 ± 1.0(14) 5.26(14) 5.7 ± 0.3(14)
ARA-VUV LMR RF Theoretical calc. VUV-LIF
[2] [7] [8] [9] This work
Ne
4.0 ± 0.5(14) 9.85(17) 68(16)
ARA-VUV Theoretical calc. VUV-LIF
[2] [9] This work
Ar
1.1 ± 0.3(12) 61.0(14) 61.0(14) 62.7(15) 3.0 ± 1.0(16) 1.96(17) 65(16)
ARA-VUV ARA-IR LMR LMR RF Theoretical calc. VUV-LIF
[2] [4] [5] [6] [8] [9] This work
Rate constants in units of cm3 molecule1 s1 are given as a (b) ” a · 10b. The quoted errors include 2-r statistical errors and some systematic uncertainties. b Experimental technique used for determination of the rate constants. ARA-VUV, atomic resonance absorption detection in the VUV; ARA-IR, atomic resonance absorption detection in the IR, LMR; laser magnetic resonance detection; RF, resonance fluorescence; VUV-LIF, Laser-induced fluorescence detection in VUV; Theoretical calc., theoretical calculations using ab initio potential curves. a
with the 193 nm pulsed laser (Lambda Physik, Compex 102). The quantum yields of the Cl* and Cl atoms in the photolysis of HCl at 193 nm were reported to be 0.41 and 0.59, respectively [13]. The Cl* atoms were detected using the VUV-LIF spectroscopy at 135.17 nm corresponding to the 4s2P1/2 ! 3p2P1/2 transition. The tunable VUV radiation was generated by two-photon resonance four-wave difference frequency mixing (2x1– x2) in krypton gas (20 Torr) [14], using two tunable dye lasers pumped simultaneously by an XeCl excimer laser (Lambda Physik, FL 3002, Scanmate 2E and Compex 201). The output of one dye laser was frequencydoubled using a BBO crystal to generate k1 = 212.56 nm, which is two-photon resonant with the 5p[1/2]0–1S0 transition of Kr. The second dye laser generated k2 498 nm. The laser beams for the four-wave mixing were focused (f = 200 mm) into a stainless steel cell containing Kr and emerged through an LiF window into the reaction chamber where the VUV laser crossed with the 193 nm laser beam at right angles. The delay time between the pump and probe laser pulses was controlled by a pulse generator (Stanford Research, DG535). The VUV-LIF signal was detected using a solar-blind photo-
multiplier tube (EMR, 541J-08-17). The output of the photomultiplier was preamplified and averaged over 10 laser pulses using a gated integrator (Stanford Research, SR-250). Reagents of N2 (Iwatani Gas, 99.999%), He (Iwatani Gas, 99.99995%), Ne (Toyo Sanso, 99.999%), Ar (Nihon Sanso, 99.999%) and HCl (Sumitomo Seika, 99.8%) were obtained commercially and were used in the experiments without further purification.
3. Results and discussion A typical temporal profile observed is shown in Fig. 1, in which 22 mTorr of HCl was photolysed at 193 nm in the presence of 70 and 280 Torr of He and the Cl* atoms were monitored using the VUV-LIF technique at 135.166 nm. The fast rise due to the photolytic Cl* formation and the following slower decay due to physical quenching in collisions with He are observed. Since the radiative lifetime of Cl* is very long (83 s) [15], the effect of radiative decay on the time profiles of Cl* can be ignored. The total removal rate constant (sum of relaxation and reaction) for Cl* + HCl collision was reported to be (7.8 ± 0.8) · 1012 cm3 molecule1 s1 [11]. Under our experimental conditions, the pseudo-first-order rate of removal of Cl* atoms via relaxation and/or reaction with HCl was about 5500 s1. We observed that the temporal decay curves of Cl* atoms for all quenchers studied here follows pseudo-first-order kinetics. Fig. 2 shows the plots of the decay rates of Cl* atoms versus the pressures of He and N2. The straight lines drawn in Fig. 2 are the results of weighted least-squares fits analysis, and the slopes give the rate constants for physical quenching of Cl*. In the error analysis for the
Cl* + He
LIF intensity / arb.
260
0
10 Delay time / µs
20
Fig. 1. Temporal profiles of the Cl* concentration after the photodissociation of HCl at 193 nm. The partial pressures are 22 mTorr for HCl and 70 Torr (open squares) and 280 Torr (open circles) for He. The solid curves are exponential decay fit to the Cl* time profiles. The Cl* atoms were detected with the technique of vacuum UV laserinduced fluorescence spectroscopy at 135.17 nm.
Rate / 106 s−1
F. Taketani et al. / Chemical Physics Letters 406 (2005) 259–262
1
He
Rate / 105 s−1
0
N2 1
0 0
1
2
[M] / 1019 molecules cm−3 Fig. 2. Plots of decay rates of Cl* atoms versus the partial pressures of He (filled circles) and N2 (open circles). Straight lines indicate the results of the weighted least-squares fits analysis, and the slopes correspond to the rate constants for physical quenching of Cl*. Error bars indicate two-sigma deviations.
rate constants, random errors in the fluorescence decay rate measurements, upper limit of the systematic errors (2%) and the precision of the mass flow controllers and pressure gage (2%) have been taken into account. The effects of the impurities in reagents cylinders, CH4, O2, H2, N2, He, H2O, CO and CO2, have also been taken into account, using the reported quenching rate constants of Cl* by those gases [3–5,7,10,16]. The uncertainties due to the impurity gases were estimated using their maximum possible concentrations which were stated by gas cylinder suppliers. Since the Cl* decay rates obtained for Ar and Ne were comparable with those estimated by the impurity gases, only the upper limit values of the rate constants for physical quenching of Cl* in collisions with Ne and Ar have been determined in this study. The rate constants obtained for physical quenching of Cl* by N2 and Rg are listed in Table 1, in which quoted uncertainties are two-standard deviations from the weighted least-squares fits. This is the first application of the VUV-LIF technique to study the absolute rate constants for physical quenching of Cl* with He and N2 at room temperature. The rate constants determined for Cl* + N2 and Cl* + He in this study are close to those obtained by Tyndall et al. [8] using the RF detection technique. Burcl et al. [9] presented theoretical values for the quenching rate constants of Cl* in collisions with He, Ne and Ar by calculating the ab initio potential
261
surfaces and non-adiabatic transition probabilities. The quenching rate constant determined for Cl* + He in the present study is slightly higher than their theoretical value. The quenching rate constants determined for Cl* with the rare gas atoms in this study become smaller in the order of mass weight of the rare gas atoms, that is, kq(He) > kq(Ne) > kq(Ar). This tendency of the quenching rate constants for the rare gas atoms is consistent with the results of the theoretical calculations by Burcl et al. A similar tendency was also reported for the physical quenching of Br(2P1/2) (denoted as Br*) to Br(2P3/2) (denoted at Br) in collisions with rare gas atoms. The energy separation between the two spin–orbit states Br and Br* is 3685 cm1. Johnson et al. [17] experimentally determined the rate constants of the physical quenching of Br* at room temperature to be (1.6 ± 0.3) · 1014, (1.1 ± 0.3) · 1014 and (6.0 ± 0.4) · 1015 cm3 molecule1 s1 for collision partners of He, Ne and Ar, respectively. These results suggest that the mechanism of physical quenching for Cl* and Br* by Rg is similar to each other. The small rate constant determined for quenching of Cl* by N2 in this study is in agreement with that reported by Tyndall et al. [8], as shown in Table 1. Since the fundamental vibrational frequency of N2 is 2359.61 cm1 [18], the electronic-to-vibrational (E–V) energy transfer process between Cl* and N2 is endothermic by 1478 cm1. The small rate constant for quenching of Cl* by N2 should be explained by ineffective electronic-to-translational (E–T) energy transfer processes.
Acknowledgements This work was supported in part by the Grant-inAids from the Ministry of Education, Culture, Sports, Science and Technology, Japan. The research grant for Dynamics of the Sun–Earth–Life Interactive System, No. G-4, the 21st Century COE Program from the Ministry is also acknowledged. This work was also supported in part by the Mitsubishi Chemical Corporation Fund (K.T.) and the Steel Industrial Foundation for the Advancement of Environmental Protection Technology (Y.M.).
References [1] I.S. Fletcher, D. Husain, Chem. Phys. Lett. 49 (1977) 516. [2] I.S. Fletcher, D. Husain, J. Chem. Soc., Faraday Trans. 74 (2) (1978) 203. [3] R.H. Clark, D. Husain, J. Chem. Soc., Faraday Trans. 80 (2) (1984) 97. [4] S.A. Sotnichenko, V.Ch. Bokun, A.I. Nadkhin, Chem. Phys. Lett. 153 (1988) 560.
262
F. Taketani et al. / Chemical Physics Letters 406 (2005) 259–262
[5] A.I. Chichinin, L.N. Krasnoperov, Chem. Phys. Lett. 124 (1986) 8. [6] S.A. Chasovnikov, A.I. Chichinin, L.N. Krasnoperov, Chem. Phys. 116 (1987) 91. [7] A.I. Chichinin, Chem. Phys. Rep. 15 (1996) 843. [8] G.S. Tyndall, J.J. Orlando, C.S. Kegley-Owen, J. Chem. Soc., Faraday Trans. 91 (1995) 3055. [9] R. Burcl, R.V. Krems, A.A. Buchachenko, M.M. Szczeßs´niak, G. Chałasin´ski, S.M. Cybulski, J. Chem. Phys. 109 (1998) 2144. [10] Y. Matsumi, K. Izumi, V. Skorokhodov, M. Kawasaki, N. Tanaka, J. Phys. Chem. A 101 (1997) 1216. [11] K. Hitsuda, K. Takahashi, Y. Matsumi, T.J. Wallington, J. Phys. Chem. A 105 (2001) 5131.
[12] K. Hitsuda, K. Takahashi, Y. Matsumi, T.J. Wallington, Chem. Phys. Lett. 346 (2001) 16. [13] J. Zhang, M. Dulligan, C. Wittig, J. Chem. Phys. 107 (1997) 1403. [14] R. Hilbig, R. Wallenstein, IEEE J. Quantum Elect. QE-19 (1983) 1759. [15] R.J. Donovan, D. Husain, Chem. Rev. 70 (1970) 489. [16] A.I. Chichinin, L.N. Krasnoperov, Chem. Phys. Lett. 160 (1989) 448. [17] R.O. Johnson, G.P. Perram, W.B. Roh, J. Chem. Phys. 104 (1996) 7052. [18] G. Herzberg, Molecular Spectra and Molecular Structure, IV. Constants of Diatomic Molecules, Van Nostrand Reinhold, New York, 1979.
Laser-induced fluorescence study of the quenching of Cl(2P1/2) in collisions with N2 molecules and rare gas atoms Fumikazu Taketani, Aya Yamasaki, Kenshi Takahashi, Yutaka Matsumi
*
Solar–Terrestrial Environment Laboratory and Graduate School of Science, Nagoya University, 3-13 Honohara, Toyokawa, Aichi 442-8507, Japan Received 30 January 2005; in final form 3 March 2005 Available online 23 March 2005
Abstract The rate constants of physical quenching of Cl(2P1/2) in collisions with N2 molecules and rare gas atoms (Rg = He, Ne and Ar) at 295 ± 2 K were investigated using a technique of vacuum ultraviolet laser-induced fluorescence spectroscopy. The rate constants determined are (7.6 ± 0.8) · 1015, (5.7 ± 0.3) · 1014, 68 · 1016 and 65 · 1016 cm3 molecule1 s1 for collision partners of N2, He, Ne and Ar, respectively. 2005 Elsevier B.V. All rights reserved.
1. Introduction The spin–orbit states of Cl(2P3/2) (denoted Cl) and Cl(2P1/2) (denoted Cl*) are separated in energy by 882 cm1, with the Cl* being higher in energy. The relaxation processes of Cl* in collisions with small molecules and rare gas atoms have been studied with a variety of experimental techniques such as atomic resonance absorption spectroscopy in the VUV (ARA-VUV) [1–3], atomic resonance absorption spectroscopy in the IR region (ARA-IR) [4], laser magnetic resonance (LMR) [5–7] and resonance fluorescence spectroscopy with an atomic resonance lamp (RF) [8]. Quantum chemical calculations have also been performed to investigate the potential energy curves for the lowest adiabatic states X2R and A2P of Cl–Rg complexes and to estimate the quenching cross-sections of Cl* in collisions with rare gas atoms (Rg) [9]. The rate constants reported previously are summarized in Table 1. In this work, the vacuum ultraviolet laser-induced fluorescence spectroscopy (VUV-LIF) have been applied to the experimental studies to determine the rate con*
Corresponding author. Fax: +81 533 89 5593. E-mail address: [email protected] (Y. Matsumi).
0009-2614/$ - see front matter 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.cplett.2005.03.003
stants of the physical quenching of Cl* atom in collisions with N2 molecules and rare gas atoms (Rg = He, Ne and Ar) at 295 ± 2 K. HCl molecules in the presence of excess N2 or Rg were irradiated with the 193 nm laser light. The temporal decay profiles of the Cl* atom produced from HCl photolysis were detected by the VUVLIF technique at 135.17 nm. The room temperature rate constants determined are compared with the available literature values.
2. Experimental section The experimental setup used in this work is essentially the same as in our previous studies on the photochemical reaction processes of Cl* and Cl [10–12]. Therefore, only a brief description related to this work will be given here. All the experiments were performed at 295 ± 2 K. The gas mixtures of a small amount of HCl and an excess of N2 or Rg were slowly introduced into the chamber through mass flow controllers. The total pressure in the cell was measured by a capacitance manometer (MKS, Baratron 622A). The reaction chamber was evacuated continuously by a rotary pump through a liquid N2 trap. The gas mixtures were irradiated
F. Taketani et al. / Chemical Physics Letters 406 (2005) 259–262
Table 1 Rate constants of the physical quenching processes of Cl* in collisions with N2 and rare gas atoms (He, Ne and Ar) at room temperature Collision partner
ka
Techniqueb
Reference
N2
6.3 ± 1.0(13) 4.0 ± 1.0(13) 3.9 ± 1.5(14) 5.0 ± 1.5(15) 7.6 ± 0.8(15)
ARA-VUV ARA-IR LMR RF VUV-LIF
[3] [4] [7] [8] This work
He
3.8 ± 0.6(15) 7.3 ± 2.0(14) 6.0 ± 1.0(14) 5.26(14) 5.7 ± 0.3(14)
ARA-VUV LMR RF Theoretical calc. VUV-LIF
[2] [7] [8] [9] This work
Ne
4.0 ± 0.5(14) 9.85(17) 68(16)
ARA-VUV Theoretical calc. VUV-LIF
[2] [9] This work
Ar
1.1 ± 0.3(12) 61.0(14) 61.0(14) 62.7(15) 3.0 ± 1.0(16) 1.96(17) 65(16)
ARA-VUV ARA-IR LMR LMR RF Theoretical calc. VUV-LIF
[2] [4] [5] [6] [8] [9] This work
Rate constants in units of cm3 molecule1 s1 are given as a (b) ” a · 10b. The quoted errors include 2-r statistical errors and some systematic uncertainties. b Experimental technique used for determination of the rate constants. ARA-VUV, atomic resonance absorption detection in the VUV; ARA-IR, atomic resonance absorption detection in the IR, LMR; laser magnetic resonance detection; RF, resonance fluorescence; VUV-LIF, Laser-induced fluorescence detection in VUV; Theoretical calc., theoretical calculations using ab initio potential curves. a
with the 193 nm pulsed laser (Lambda Physik, Compex 102). The quantum yields of the Cl* and Cl atoms in the photolysis of HCl at 193 nm were reported to be 0.41 and 0.59, respectively [13]. The Cl* atoms were detected using the VUV-LIF spectroscopy at 135.17 nm corresponding to the 4s2P1/2 ! 3p2P1/2 transition. The tunable VUV radiation was generated by two-photon resonance four-wave difference frequency mixing (2x1– x2) in krypton gas (20 Torr) [14], using two tunable dye lasers pumped simultaneously by an XeCl excimer laser (Lambda Physik, FL 3002, Scanmate 2E and Compex 201). The output of one dye laser was frequencydoubled using a BBO crystal to generate k1 = 212.56 nm, which is two-photon resonant with the 5p[1/2]0–1S0 transition of Kr. The second dye laser generated k2 498 nm. The laser beams for the four-wave mixing were focused (f = 200 mm) into a stainless steel cell containing Kr and emerged through an LiF window into the reaction chamber where the VUV laser crossed with the 193 nm laser beam at right angles. The delay time between the pump and probe laser pulses was controlled by a pulse generator (Stanford Research, DG535). The VUV-LIF signal was detected using a solar-blind photo-
multiplier tube (EMR, 541J-08-17). The output of the photomultiplier was preamplified and averaged over 10 laser pulses using a gated integrator (Stanford Research, SR-250). Reagents of N2 (Iwatani Gas, 99.999%), He (Iwatani Gas, 99.99995%), Ne (Toyo Sanso, 99.999%), Ar (Nihon Sanso, 99.999%) and HCl (Sumitomo Seika, 99.8%) were obtained commercially and were used in the experiments without further purification.
3. Results and discussion A typical temporal profile observed is shown in Fig. 1, in which 22 mTorr of HCl was photolysed at 193 nm in the presence of 70 and 280 Torr of He and the Cl* atoms were monitored using the VUV-LIF technique at 135.166 nm. The fast rise due to the photolytic Cl* formation and the following slower decay due to physical quenching in collisions with He are observed. Since the radiative lifetime of Cl* is very long (83 s) [15], the effect of radiative decay on the time profiles of Cl* can be ignored. The total removal rate constant (sum of relaxation and reaction) for Cl* + HCl collision was reported to be (7.8 ± 0.8) · 1012 cm3 molecule1 s1 [11]. Under our experimental conditions, the pseudo-first-order rate of removal of Cl* atoms via relaxation and/or reaction with HCl was about 5500 s1. We observed that the temporal decay curves of Cl* atoms for all quenchers studied here follows pseudo-first-order kinetics. Fig. 2 shows the plots of the decay rates of Cl* atoms versus the pressures of He and N2. The straight lines drawn in Fig. 2 are the results of weighted least-squares fits analysis, and the slopes give the rate constants for physical quenching of Cl*. In the error analysis for the
Cl* + He
LIF intensity / arb.
260
0
10 Delay time / µs
20
Fig. 1. Temporal profiles of the Cl* concentration after the photodissociation of HCl at 193 nm. The partial pressures are 22 mTorr for HCl and 70 Torr (open squares) and 280 Torr (open circles) for He. The solid curves are exponential decay fit to the Cl* time profiles. The Cl* atoms were detected with the technique of vacuum UV laserinduced fluorescence spectroscopy at 135.17 nm.
Rate / 106 s−1
F. Taketani et al. / Chemical Physics Letters 406 (2005) 259–262
1
He
Rate / 105 s−1
0
N2 1
0 0
1
2
[M] / 1019 molecules cm−3 Fig. 2. Plots of decay rates of Cl* atoms versus the partial pressures of He (filled circles) and N2 (open circles). Straight lines indicate the results of the weighted least-squares fits analysis, and the slopes correspond to the rate constants for physical quenching of Cl*. Error bars indicate two-sigma deviations.
rate constants, random errors in the fluorescence decay rate measurements, upper limit of the systematic errors (2%) and the precision of the mass flow controllers and pressure gage (2%) have been taken into account. The effects of the impurities in reagents cylinders, CH4, O2, H2, N2, He, H2O, CO and CO2, have also been taken into account, using the reported quenching rate constants of Cl* by those gases [3–5,7,10,16]. The uncertainties due to the impurity gases were estimated using their maximum possible concentrations which were stated by gas cylinder suppliers. Since the Cl* decay rates obtained for Ar and Ne were comparable with those estimated by the impurity gases, only the upper limit values of the rate constants for physical quenching of Cl* in collisions with Ne and Ar have been determined in this study. The rate constants obtained for physical quenching of Cl* by N2 and Rg are listed in Table 1, in which quoted uncertainties are two-standard deviations from the weighted least-squares fits. This is the first application of the VUV-LIF technique to study the absolute rate constants for physical quenching of Cl* with He and N2 at room temperature. The rate constants determined for Cl* + N2 and Cl* + He in this study are close to those obtained by Tyndall et al. [8] using the RF detection technique. Burcl et al. [9] presented theoretical values for the quenching rate constants of Cl* in collisions with He, Ne and Ar by calculating the ab initio potential
261
surfaces and non-adiabatic transition probabilities. The quenching rate constant determined for Cl* + He in the present study is slightly higher than their theoretical value. The quenching rate constants determined for Cl* with the rare gas atoms in this study become smaller in the order of mass weight of the rare gas atoms, that is, kq(He) > kq(Ne) > kq(Ar). This tendency of the quenching rate constants for the rare gas atoms is consistent with the results of the theoretical calculations by Burcl et al. A similar tendency was also reported for the physical quenching of Br(2P1/2) (denoted as Br*) to Br(2P3/2) (denoted at Br) in collisions with rare gas atoms. The energy separation between the two spin–orbit states Br and Br* is 3685 cm1. Johnson et al. [17] experimentally determined the rate constants of the physical quenching of Br* at room temperature to be (1.6 ± 0.3) · 1014, (1.1 ± 0.3) · 1014 and (6.0 ± 0.4) · 1015 cm3 molecule1 s1 for collision partners of He, Ne and Ar, respectively. These results suggest that the mechanism of physical quenching for Cl* and Br* by Rg is similar to each other. The small rate constant determined for quenching of Cl* by N2 in this study is in agreement with that reported by Tyndall et al. [8], as shown in Table 1. Since the fundamental vibrational frequency of N2 is 2359.61 cm1 [18], the electronic-to-vibrational (E–V) energy transfer process between Cl* and N2 is endothermic by 1478 cm1. The small rate constant for quenching of Cl* by N2 should be explained by ineffective electronic-to-translational (E–T) energy transfer processes.
Acknowledgements This work was supported in part by the Grant-inAids from the Ministry of Education, Culture, Sports, Science and Technology, Japan. The research grant for Dynamics of the Sun–Earth–Life Interactive System, No. G-4, the 21st Century COE Program from the Ministry is also acknowledged. This work was also supported in part by the Mitsubishi Chemical Corporation Fund (K.T.) and the Steel Industrial Foundation for the Advancement of Environmental Protection Technology (Y.M.).
References [1] I.S. Fletcher, D. Husain, Chem. Phys. Lett. 49 (1977) 516. [2] I.S. Fletcher, D. Husain, J. Chem. Soc., Faraday Trans. 74 (2) (1978) 203. [3] R.H. Clark, D. Husain, J. Chem. Soc., Faraday Trans. 80 (2) (1984) 97. [4] S.A. Sotnichenko, V.Ch. Bokun, A.I. Nadkhin, Chem. Phys. Lett. 153 (1988) 560.
262
F. Taketani et al. / Chemical Physics Letters 406 (2005) 259–262
[5] A.I. Chichinin, L.N. Krasnoperov, Chem. Phys. Lett. 124 (1986) 8. [6] S.A. Chasovnikov, A.I. Chichinin, L.N. Krasnoperov, Chem. Phys. 116 (1987) 91. [7] A.I. Chichinin, Chem. Phys. Rep. 15 (1996) 843. [8] G.S. Tyndall, J.J. Orlando, C.S. Kegley-Owen, J. Chem. Soc., Faraday Trans. 91 (1995) 3055. [9] R. Burcl, R.V. Krems, A.A. Buchachenko, M.M. Szczeßs´niak, G. Chałasin´ski, S.M. Cybulski, J. Chem. Phys. 109 (1998) 2144. [10] Y. Matsumi, K. Izumi, V. Skorokhodov, M. Kawasaki, N. Tanaka, J. Phys. Chem. A 101 (1997) 1216. [11] K. Hitsuda, K. Takahashi, Y. Matsumi, T.J. Wallington, J. Phys. Chem. A 105 (2001) 5131.
[12] K. Hitsuda, K. Takahashi, Y. Matsumi, T.J. Wallington, Chem. Phys. Lett. 346 (2001) 16. [13] J. Zhang, M. Dulligan, C. Wittig, J. Chem. Phys. 107 (1997) 1403. [14] R. Hilbig, R. Wallenstein, IEEE J. Quantum Elect. QE-19 (1983) 1759. [15] R.J. Donovan, D. Husain, Chem. Rev. 70 (1970) 489. [16] A.I. Chichinin, L.N. Krasnoperov, Chem. Phys. Lett. 160 (1989) 448. [17] R.O. Johnson, G.P. Perram, W.B. Roh, J. Chem. Phys. 104 (1996) 7052. [18] G. Herzberg, Molecular Spectra and Molecular Structure, IV. Constants of Diatomic Molecules, Van Nostrand Reinhold, New York, 1979.