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Radiative lifetime of the Te2 B0+u and A0+u states excited by a pulsed dye laser
Volume 123, number 6
CHEMICAL PHYSICS LETTERS
31 January 1986
RADIATIVE LIFETIME OF THE Te, B O,+ AND A O,+ STATES EXCITED BY A PULSED DYE LASER William G. THORPE, W. Robert CARPER ’ Frank J. Seiler Research Laboratqv,
USAF Academy,
Colorado Sprmgs, CO 80840 - 6528. USA
and S.J. DAVIS Atr Force Weapons Laboratory, Kirtland Atr Force Base, NM 871 I7, USA Received 10 June 1985; in final form 1 October 1985
A pulsed dye laser has been used to measure the radiative lifetimes and quenching rates of transitions of the BO: and AOJ states of Te,. The observed zero pressure lifetimes vary from 55 to 730 ns. The quenching rates vary from 0.9 x 10” to 40x lo6 S -’ Torr-‘.
I. Introduction There is limited information concerning the chemistry and radiative properties of diatomic group VI fluorides [ 1,2]. At the same time, there is considerable potential in these and related systems as electronic transition chemical laser candidates. Our interest in chemiluminescent reactions as possible laser candidates, led us to measure the laser-induced fluorescence (LIF) lifetime of SeF [ 11. A similar attempt to study the LIF lifetime of TeF was unsuccessful [2], however, Te2 was seen to produce a strong fluorescence between 4180 and 5200 A. This was lnvestigated with the possibility of observing a long-lived excited state, thus offering the potential of a realistic laser candidate. Te, fluorescence was first observed using various arcs and spark discharges, including Hg, Pb, and Cd [3]. Steinfeld [4] excited Te2 vapor with a He/Cd laser operating at 4417 A. The resulting fluorescence was identified as originating at the u’ = 5 level with ’ Permanent address: Department of Chemistry, Wichita State University, Wichita, KS 67208, USA.
0 009-2614/86/$03.50 0 Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
observed transitions to the 0” = 1 through 22 levels. Initially first studied by Rosen [S1, the major band systems of Te,, A 0: to X Og’and B 0: to X O+,were examined by Barrow and DuParq in 1972 [6f. Stone and Barrow [7] subsequently ascribed a band series to the B 0: to X 1, and B 1; to X 1s transitions. Recently, Verges et al. [8] used laser-induced fluorescence to further define four upper states and three lower states of Te,. The strongest absorption bands are assigned to the A 0:-X 0: and B 0=--X 0; transitions. In this study we report the zero-pressure lifetimes and total quenching rates at four different wavelengths for Te, . The assigned transitions include B 0: -X 0; and A 0: -X 0;.
2. Experimental The experimental apparatus has been described previously [ 1,9]. The continuous scan Molectron dye laser is a nitrogen pumped dye laser with a 4 A spectral width (fwhm) and an average output of 20 CCJper pulse. Its operating range for our experiments extends from 4200 to 7 100 A. 493
Volume 123, number 6
CHEMICAL PHYSICS LETTEZRS
The PMT was an uncoobd RCA C3 1034 tube. Various long-pass filters were employed to block out scattered laser light. The PMT output was amplified by a Hewlett-Packard 462A amplifier and fed to a transient recorder. For laser excitation spectra, a Princeton Applied Research model 162 boxcar averager was used. During lifetime measurements, this was replaced by a Biomation model 6500 waveform recorder interfaced to a Nicolet model NE-80 data processor. The spectra were digitized and ~~yzed with the aid of a HP computer system con~st~g of a model 9835A computer, model 9874A digitizer, and model 9872A XY plotter. Possible systematic effects such as photomultiplier saturation and radiation trapping were minimized. Decay curves were monitored on an oscilloscope at various PMT voltages to ensure the operating voltage did not cause the tube to saturate. The aperture of the Biomation recorder was some 50 ns past the laser pulse to minimize convolution effects of the pulse. Te, was produced in the fluorescence cell by heating solid tellurium to 312OC.The dye laser beam was passed through the cell and scanned through the entire dye range. Fluorescence signals were observed in the 4200 to 5200 A region.
3. Results and discussion A typical laser-induced spectrum is shown in fig. 1.
WAVELENGTH Fig. 1. Laser
(ii,
Tez from 4750 to 5200 A. Pressure is 2.28 Torr, temperature 312’C, 5700 A long-pass filter and PMT voltage -1000 V.
494
excitation spectrafor
31 January 1986
The bandheads observed in the 4200-5200 W region have been assigned to the A 0:-X 0; and B 0:--X 0; transitions, and are given in table 1. The lifetimes and total quenching rates have been determined at four different wavelengths. Generally, the pressure was varied from 0.34 to 10 Torr by the means detailed for SeF [l]. Typical Stern-Vohner plots are given in figs. 2 and 3. The 4235 a band is assigned as the (9,0) transition between the B 0: and X 0; states. Its lifetime is found to be 5.5 ns with a total gas quenc~g rate of 1.2 X 106 s-l Torr-1. In the same band systems, the 4309 A band is assigned as the (81) transition. Its lifetime is slightly higher at 68 ns with a quenching rate of 0.9 X lo6 s-l Torr-l. The quenching rates and lifetimes are summarized in table 2. The 4897 A band is assigned as the (8,O) transition between the A 0: and X 0: states. Its lifetime is found to be quite large in comparison with those of the previous bands: 0.7 ps. The total gas quenching rate is the lowest at 0.4 X lo6 s-l Torr-l, The remaining transition at 4563 a has a lifetime closer to that of the fust two. It is most likely the (0,l) tran~tion between the B 0: and X 0: states. In comparison, the lifetime of S2 is approximately 20 ns for the B 3C; state [lo]. The fluorescence from S2 is especially strong and makes the molecule suitable for an optically or electrically pumped electronic laser, Dalby [ 1 l] has estimated a zero-pressure lifetime of 58 ns for the B 1, to X 1, transition of *0Se2. Therefore, the measured lifetime for Te, of 90 ns is quite reasonable. There is a large difference in the lifetime of the (8,0) tran~tion in the A state. The pressure had to be greater than 2 Torr for observation of lair-induced fluorescence. The potential energy levels of Te, as proposed by Rosen [5] show extensive perturbations in what was assigned as the A state. Better data which are now available [ 121 suggest that this state is actually the B state. Thus the shorter lifetimes which we observed for the transitions in the B state are due to perturbing potential curves. In addition, radiationless transitions from the B to the A state would produce a longer apparent lifetime for the A state. It is apparent that Te, is a definite laser candi- . date when compared with S, [lo]. The fluorescence of Te2 at 4897 A is stronger than that of S2 and its lifetime is considerably longer. The main weakness of Te2 as a Iasing species may lie in its quenching. These
Table 1 Laser-induced fluorescence of Tes A 0:-X
0;
B 0:-X
transition
(11,O) (lO,O) (9,O) (8,O) (7,O) (6.0) (5 ,O) (4 ,O) (3,O) (4,l) (2,O) (391) (1,O) (2J) (0,O) (1s) (0.1) (12)
observed
calculated
A (A)
h (A)
4787 4824 4855 4885 4916 4946 4981 5011 5048 5075 5082 5109 5118 5152 5160 5186 5219 5254
4782 4812 4843 4875 4907 4941 4974 5009 5044 5071 5080 5108 5117 5 144 5155 5182 5221 5249
0;
transition
(10,O) (11.1) (9,O) (10.1) WI (9,l) (7 ,O) (8,l) (60) (7,1) (5 ,O) (6.1) (4,O) (5,l) (3,O) (431) (2,O) (3,l) (2,2) (OJ) (1,2) (2,3) (1,O) (2,1) (W) (1,l)
.OJO
observed
calculated
h (A)
A (A)
4206 4220 4231 4249 4258 4277 4289
4215 4232 4242 4259 4269 4286 4297 4314 4326 4343 4355 4372 4385 4402 4416 4433 4447 4464 4546 4562 4580 4597 4479 4496 4512 4529
4303 4315 4332 4349 4363 4376 4393 4408 4426 4440 4454 4539 4554 4572 4588 4473 4491 4504 4518
2.6
3.2
2.6
i
-
.024
0 s E
-,
2.4
2
.022
_y
20.
t ’ L 3
4235
.014
i
4897
0.6
A
0.4
.012
.OlO
16.
0
2
4
6
a
PRESSURE(TORR) Fig. 2. Stem-Volmer plot for Te2 at 4235 A. 27 data sets, zero-pressure lifetime is 55 ns for the (9,O) band of B-X transition.
0 0
1
2
3
4
5
PRESSUREtTORR)
Fig. 3. Stem-Volmer plot for Te2 at 4897 A. 19 data sets, zero-pressure lifetime is 700 ns for the (8,0) band of the A-X transition. Fluorescence not observed below 2 Torr.
CHEMICAL PHYSICS LETTERS
Volume 123, number 6
References
Table 2 Quenching rates and lifetimes for Tea A (w-49 (A)
Transition excited
Total product quenching rate a)
Zero-pressure lifetime b,
4235 4309 4563 4897
(9s)) c, (8,l) ‘) (0,l) c, (8 ,O) d,
(1.2 (0.9 (1.3 (4.0
55.2 67.6 90 f 730 f
f f * f
0.1) 0.1) 0.6) 0.1)
x x X x
106 106 lo6 10s
f 0.7 f 1.1 5 55
a)Quoted
errors repr e sent one standard deviation in the slope of Stern-Volmer plots. Units are s-l Torr-' . b, Quoted errors represe nt one standard deviation in the interceuts of Stern-Vohner nlots. Units are ns. ‘1B 0:-X 0;. d, A 0:-x 0;.
and other questions can only be answered by additional experimentation with Te,.
Acknowledgement The authors gratefully acknowledge the generous assistance of Gregg Bradbum and the entire staff at the Air Force Weapons Laboratory. WRC is indebted to the Air Force URRF’program and the National Research Council for fellowships.
496
31 January 1986
[ 1] W.G. Thorpe, W.R. Carper and S J. Davis, J. Chem. Phys., to be published. [2] W.G. Thorpe, W.R. Carper and S J. Davis, J. Chem. Phys., to be published. [ 31 P. Prhrgsheim, Fluorescence and phosphorescence (Interscience, New York, 1949). [4] J.I. Steinfeld, Molecules and radiation (Harper and Row, New York, 1974). [S] B. Rosen, Naturwissenschaften 14 (1926) 978. [6] R.F. Barrow and R.P. DuParq, Proc. Roy. Sot. A327 (1972) 279. [7] T.J. Stone and R.F. Barrow, Can. J. Phys. 53 (1975) 1976. [8] J. Verges, C. Effantin, 0. Babaky, J. Dlncan, S.J. Prosser and R.F. Barrow, Physics Scripta 25 (1982) 338. [9] G.R. Bradburn, R.A. Armstrong and S.J. Davis, J. Chem. Phys. 71(1979) 2250. [lo] S.R. Leone and K.G. Ikosnik, Appl. Phys. Letters 30 (1977) 346. [ 1 l] F.W. DaIby, J. Vigue and J.C. Lehmann, Can. J. Phys. 53 (1975) 140. [12] S.N. Suchard, Spectroscopic constants for selected heteronuclear molecules, Vols. I-III, Rept. No. TRaO74 (4641)-6, The Aerospace Corp., El Segundo (1974).
CHEMICAL PHYSICS LETTERS
31 January 1986
RADIATIVE LIFETIME OF THE Te, B O,+ AND A O,+ STATES EXCITED BY A PULSED DYE LASER William G. THORPE, W. Robert CARPER ’ Frank J. Seiler Research Laboratqv,
USAF Academy,
Colorado Sprmgs, CO 80840 - 6528. USA
and S.J. DAVIS Atr Force Weapons Laboratory, Kirtland Atr Force Base, NM 871 I7, USA Received 10 June 1985; in final form 1 October 1985
A pulsed dye laser has been used to measure the radiative lifetimes and quenching rates of transitions of the BO: and AOJ states of Te,. The observed zero pressure lifetimes vary from 55 to 730 ns. The quenching rates vary from 0.9 x 10” to 40x lo6 S -’ Torr-‘.
I. Introduction There is limited information concerning the chemistry and radiative properties of diatomic group VI fluorides [ 1,2]. At the same time, there is considerable potential in these and related systems as electronic transition chemical laser candidates. Our interest in chemiluminescent reactions as possible laser candidates, led us to measure the laser-induced fluorescence (LIF) lifetime of SeF [ 11. A similar attempt to study the LIF lifetime of TeF was unsuccessful [2], however, Te2 was seen to produce a strong fluorescence between 4180 and 5200 A. This was lnvestigated with the possibility of observing a long-lived excited state, thus offering the potential of a realistic laser candidate. Te, fluorescence was first observed using various arcs and spark discharges, including Hg, Pb, and Cd [3]. Steinfeld [4] excited Te2 vapor with a He/Cd laser operating at 4417 A. The resulting fluorescence was identified as originating at the u’ = 5 level with ’ Permanent address: Department of Chemistry, Wichita State University, Wichita, KS 67208, USA.
0 009-2614/86/$03.50 0 Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
observed transitions to the 0” = 1 through 22 levels. Initially first studied by Rosen [S1, the major band systems of Te,, A 0: to X Og’and B 0: to X O+,were examined by Barrow and DuParq in 1972 [6f. Stone and Barrow [7] subsequently ascribed a band series to the B 0: to X 1, and B 1; to X 1s transitions. Recently, Verges et al. [8] used laser-induced fluorescence to further define four upper states and three lower states of Te,. The strongest absorption bands are assigned to the A 0:-X 0: and B 0=--X 0; transitions. In this study we report the zero-pressure lifetimes and total quenching rates at four different wavelengths for Te, . The assigned transitions include B 0: -X 0; and A 0: -X 0;.
2. Experimental The experimental apparatus has been described previously [ 1,9]. The continuous scan Molectron dye laser is a nitrogen pumped dye laser with a 4 A spectral width (fwhm) and an average output of 20 CCJper pulse. Its operating range for our experiments extends from 4200 to 7 100 A. 493
Volume 123, number 6
CHEMICAL PHYSICS LETTEZRS
The PMT was an uncoobd RCA C3 1034 tube. Various long-pass filters were employed to block out scattered laser light. The PMT output was amplified by a Hewlett-Packard 462A amplifier and fed to a transient recorder. For laser excitation spectra, a Princeton Applied Research model 162 boxcar averager was used. During lifetime measurements, this was replaced by a Biomation model 6500 waveform recorder interfaced to a Nicolet model NE-80 data processor. The spectra were digitized and ~~yzed with the aid of a HP computer system con~st~g of a model 9835A computer, model 9874A digitizer, and model 9872A XY plotter. Possible systematic effects such as photomultiplier saturation and radiation trapping were minimized. Decay curves were monitored on an oscilloscope at various PMT voltages to ensure the operating voltage did not cause the tube to saturate. The aperture of the Biomation recorder was some 50 ns past the laser pulse to minimize convolution effects of the pulse. Te, was produced in the fluorescence cell by heating solid tellurium to 312OC.The dye laser beam was passed through the cell and scanned through the entire dye range. Fluorescence signals were observed in the 4200 to 5200 A region.
3. Results and discussion A typical laser-induced spectrum is shown in fig. 1.
WAVELENGTH Fig. 1. Laser
(ii,
Tez from 4750 to 5200 A. Pressure is 2.28 Torr, temperature 312’C, 5700 A long-pass filter and PMT voltage -1000 V.
494
excitation spectrafor
31 January 1986
The bandheads observed in the 4200-5200 W region have been assigned to the A 0:-X 0; and B 0:--X 0; transitions, and are given in table 1. The lifetimes and total quenching rates have been determined at four different wavelengths. Generally, the pressure was varied from 0.34 to 10 Torr by the means detailed for SeF [l]. Typical Stern-Vohner plots are given in figs. 2 and 3. The 4235 a band is assigned as the (9,0) transition between the B 0: and X 0; states. Its lifetime is found to be 5.5 ns with a total gas quenc~g rate of 1.2 X 106 s-l Torr-1. In the same band systems, the 4309 A band is assigned as the (81) transition. Its lifetime is slightly higher at 68 ns with a quenching rate of 0.9 X lo6 s-l Torr-l. The quenching rates and lifetimes are summarized in table 2. The 4897 A band is assigned as the (8,O) transition between the A 0: and X 0: states. Its lifetime is found to be quite large in comparison with those of the previous bands: 0.7 ps. The total gas quenching rate is the lowest at 0.4 X lo6 s-l Torr-l, The remaining transition at 4563 a has a lifetime closer to that of the fust two. It is most likely the (0,l) tran~tion between the B 0: and X 0: states. In comparison, the lifetime of S2 is approximately 20 ns for the B 3C; state [lo]. The fluorescence from S2 is especially strong and makes the molecule suitable for an optically or electrically pumped electronic laser, Dalby [ 1 l] has estimated a zero-pressure lifetime of 58 ns for the B 1, to X 1, transition of *0Se2. Therefore, the measured lifetime for Te, of 90 ns is quite reasonable. There is a large difference in the lifetime of the (8,0) tran~tion in the A state. The pressure had to be greater than 2 Torr for observation of lair-induced fluorescence. The potential energy levels of Te, as proposed by Rosen [5] show extensive perturbations in what was assigned as the A state. Better data which are now available [ 121 suggest that this state is actually the B state. Thus the shorter lifetimes which we observed for the transitions in the B state are due to perturbing potential curves. In addition, radiationless transitions from the B to the A state would produce a longer apparent lifetime for the A state. It is apparent that Te, is a definite laser candi- . date when compared with S, [lo]. The fluorescence of Te2 at 4897 A is stronger than that of S2 and its lifetime is considerably longer. The main weakness of Te2 as a Iasing species may lie in its quenching. These
Table 1 Laser-induced fluorescence of Tes A 0:-X
0;
B 0:-X
transition
(11,O) (lO,O) (9,O) (8,O) (7,O) (6.0) (5 ,O) (4 ,O) (3,O) (4,l) (2,O) (391) (1,O) (2J) (0,O) (1s) (0.1) (12)
observed
calculated
A (A)
h (A)
4787 4824 4855 4885 4916 4946 4981 5011 5048 5075 5082 5109 5118 5152 5160 5186 5219 5254
4782 4812 4843 4875 4907 4941 4974 5009 5044 5071 5080 5108 5117 5 144 5155 5182 5221 5249
0;
transition
(10,O) (11.1) (9,O) (10.1) WI (9,l) (7 ,O) (8,l) (60) (7,1) (5 ,O) (6.1) (4,O) (5,l) (3,O) (431) (2,O) (3,l) (2,2) (OJ) (1,2) (2,3) (1,O) (2,1) (W) (1,l)
.OJO
observed
calculated
h (A)
A (A)
4206 4220 4231 4249 4258 4277 4289
4215 4232 4242 4259 4269 4286 4297 4314 4326 4343 4355 4372 4385 4402 4416 4433 4447 4464 4546 4562 4580 4597 4479 4496 4512 4529
4303 4315 4332 4349 4363 4376 4393 4408 4426 4440 4454 4539 4554 4572 4588 4473 4491 4504 4518
2.6
3.2
2.6
i
-
.024
0 s E
-,
2.4
2
.022
_y
20.
t ’ L 3
4235
.014
i
4897
0.6
A
0.4
.012
.OlO
16.
0
2
4
6
a
PRESSURE(TORR) Fig. 2. Stem-Volmer plot for Te2 at 4235 A. 27 data sets, zero-pressure lifetime is 55 ns for the (9,O) band of B-X transition.
0 0
1
2
3
4
5
PRESSUREtTORR)
Fig. 3. Stem-Volmer plot for Te2 at 4897 A. 19 data sets, zero-pressure lifetime is 700 ns for the (8,0) band of the A-X transition. Fluorescence not observed below 2 Torr.
CHEMICAL PHYSICS LETTERS
Volume 123, number 6
References
Table 2 Quenching rates and lifetimes for Tea A (w-49 (A)
Transition excited
Total product quenching rate a)
Zero-pressure lifetime b,
4235 4309 4563 4897
(9s)) c, (8,l) ‘) (0,l) c, (8 ,O) d,
(1.2 (0.9 (1.3 (4.0
55.2 67.6 90 f 730 f
f f * f
0.1) 0.1) 0.6) 0.1)
x x X x
106 106 lo6 10s
f 0.7 f 1.1 5 55
a)Quoted
errors repr e sent one standard deviation in the slope of Stern-Volmer plots. Units are s-l Torr-' . b, Quoted errors represe nt one standard deviation in the interceuts of Stern-Vohner nlots. Units are ns. ‘1B 0:-X 0;. d, A 0:-x 0;.
and other questions can only be answered by additional experimentation with Te,.
Acknowledgement The authors gratefully acknowledge the generous assistance of Gregg Bradbum and the entire staff at the Air Force Weapons Laboratory. WRC is indebted to the Air Force URRF’program and the National Research Council for fellowships.
496
31 January 1986
[ 1] W.G. Thorpe, W.R. Carper and S J. Davis, J. Chem. Phys., to be published. [2] W.G. Thorpe, W.R. Carper and S J. Davis, J. Chem. Phys., to be published. [ 31 P. Prhrgsheim, Fluorescence and phosphorescence (Interscience, New York, 1949). [4] J.I. Steinfeld, Molecules and radiation (Harper and Row, New York, 1974). [S] B. Rosen, Naturwissenschaften 14 (1926) 978. [6] R.F. Barrow and R.P. DuParq, Proc. Roy. Sot. A327 (1972) 279. [7] T.J. Stone and R.F. Barrow, Can. J. Phys. 53 (1975) 1976. [8] J. Verges, C. Effantin, 0. Babaky, J. Dlncan, S.J. Prosser and R.F. Barrow, Physics Scripta 25 (1982) 338. [9] G.R. Bradburn, R.A. Armstrong and S.J. Davis, J. Chem. Phys. 71(1979) 2250. [lo] S.R. Leone and K.G. Ikosnik, Appl. Phys. Letters 30 (1977) 346. [ 1 l] F.W. DaIby, J. Vigue and J.C. Lehmann, Can. J. Phys. 53 (1975) 140. [12] S.N. Suchard, Spectroscopic constants for selected heteronuclear molecules, Vols. I-III, Rept. No. TRaO74 (4641)-6, The Aerospace Corp., El Segundo (1974).