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The emission spectrum of C2N2
Volume I6 I,
number 3
CHEMICAL PHYSICS LETTERS
15 September 1989
THE EMISSION SPECTRUM OF CZNZ Samuel A. BARTS and Joshua B. HALPERN Department of Chemistry Howard University, Washington. DC 20059. USA Received IS March 1989; in final form 30 June 1989
Cyanogen absorption, excitation and dispersed fluorescence spectra have been measured in the 220 nm region. The radiative lifetime is 1.34 us under collisionless conditions. The fluorescence spectrum following excitation of the 4; band consists of four simple progressions. No CN radical fragments were detected following absorption at 220 nm. This clearly demonstrates the bound nature of the lowest vibrational levels of the A ‘Z; electronic state. The emission could be used for remote detection of cyanogen in astronomical systems.
1. Introduction The 220 nm A ‘E; CX ‘C: transition is the lowest energy singlet absorption of cyanogen. There are two higher wavelength triplet-singlet UV transitions the a 3Zc +-X ‘Zl system at 300 nm [ 1 ] and the b’3A,t X ‘Cl system at 250 nm [ 21. Previously, emission has been observed from the first triplet system [ 31, but there is no report of singlet fluorescence. Fish et al. were able to resolve rotational structure in the bands around 220 nm but not at lower wavelengths [ 41. This suggested that it might be possible to observe the fluorescence spectrum following excitation of the lowest few vibrational levels of the A ‘2;; electronic state. Speaking against this possibility was Davis and Okabe’s bond strength measurement of 5.58kO.05 eV which implies a photodissociation limit of 222.2 &2.0 nm [ 5 1. However, more recently Eres, Gumick and McDonald measured CN radical quantum state distributions after the photolysis of cyanogen at 193 nm [ 61. From the highest measured fragment rotational energy they derived a cyanogen bond energy of 5.83 to.04 eV and a photodissociation limit of 212.7+ 1.3 nm. Lin, Johnston and Jackson have studied the photodissociation of cyanogen at 206 nm using a doubled dye laser as the photolysis source [ 7 1. Based on the last CN rotational state observed they find a bond strength of 5.70 eV and a
dissociation limit of 217.5 nm. They point out that it was possible that a hot band was excited. Thus, 5.70 eV should be regarded as an upper limit and not a lower limit as stated in ref. [ 71. It should be noted that the bandwidth of their photolysis laser was 1.0 cm- ‘, while that of the ArF excimer laser used by Ems, Gumick and McDonald was about 250 cm-‘. Based on Davis and Okabe’s bond strength all lines of the cyanogen X ‘xl +A ‘I;; system will be dissociative [ 51. On the other hand, both Lin et al.‘s and Eres et al.% values for the dissociation limit imply that at least one strong transition, the 4; line at 218.87 nm, terminates in a state that is stable against dissociation. This paper reports measurements of absorption, excitation and dispersed fluorescence spectra of cyanogen in the 220 nm region. The results clearly demonstrate the bound nature of the excited upper state. The fluorescence can be used to detect the formation of cyanogen in astronomical systems such as comets and gas giant planets.
2. Experimental The experimental apparatus has been previously described [ 8 1. The emission spectrum was excited by a frequency-doubled, Nd-YAG-pumped dye laser that was shifted to the 220 nm region by four-wave mixing in 20 atm hydrogen. The third anti-Stokes
0 009-26 14/89/s 03.50 0 Elsevier Science Publishers B.V. ( North-Holland Physics Publishing Division )
207
Volume 161, number 3
15September 1989
CHEMICAL PHYSICS LETTERS
component of the Raman-shifted beams was used to excite the cyanogen. The laser has a bandwidth of 0.4 cm-’ at 600 nm, which results in a resolution of 2.0 cm- ’ or 0.01 nm after doubling and frequency shifting to 220 nm. Fluorescence was observed at right angles to the plane formed by the laser beam and the direction of its electric vector. Total fluorescence was monitored by an eleven-stage EMR VUV photomultiplier. The fluorescence was also dispersed through a 0.25 m Jobin-Yvon monochromator and detected by an eight-stage side-on Hamamatsu photomultiplier tuber. 1.0 and 0.25 mm monochromator slits produced resolutions of 4 and 1 nm in first order, respectively- The intensity of the frequency-shifted exciting light was monitored by a photodiode. The intensity of the light passing through the experimental cell was monitored by a photodiode to yield absorption spectra. Signals were integrated in a PAR model 160 boxcar analyzer. The experiment was controlled by an IBM/XT based data acquisition system designed in our laboratory. The data were recorded by the computer. Cyanogen was bought from the Matheson Co. and purified by freeze-thaw distillation. Cyanogen gas was passed through a vacuum cell at pressures between 1 Torr and 0.5 mTorr as measured by a capacitance manometer.
219.5
219.0
220.0 (nm)
22075
WAVELENGTH
Fig. 1. The excitation spectrum of cyanogen is displayed as a function of exciting light wavelength. The insert above the 4; peak shows the absorbance measured with the same source. The pressure of cyanogen in the cell for the excitation spectrum was 0.01 Torr. The absorption spectrum was measured at 1 Torr.
3. Results Fig. 1 shows the excitation spectrum in the 220 nm region. Only two bands were observed. The total fluorescence was measured while the exciting dye laser was tuned between 2 18 and 222 nm. While fig. 1 displays the total fluorescence as a function of excitation frequency, excitation spectra have also been obtained while monitoring individual fluorescence bands. Such spectra are identical in shape to that seen in fig. 1. The insert above the 4; feature shows the absorption spectrum in this region. Fig. 2 shows the dispersed fluorescence spectrum obtained when the exciting laser is fixed on the Q band head of the 218.9 nm 4; transition. The spectrum was recorded in second orderwith a resolution of 1.0 nm so the resolution of the bands is 0.5 nm. The wavelength scale was calibrated by shining a low 208
210
230
250
WAVELENGTH
270
(nm)
Fig. 2. The fluorescence spectrum of cyanogen excited at 2 18.9 nm on the 4i Q branch (largest feature in the excitation spectrum), The resolution of the scanning monochromator is 0.5 nm in second order. The cyanogen pressure was 0.12 Torr, with the gas passing slowly through the cell. The spectrum consists of four progressions as indicated in the upper part of the figure.
pressure Hg lamp into the experimental cell where a portion was scattered into the monochromator. Cyanogen fluorescence band positions were obtained by interpolation between first- and second-order lines of Hg. The cyanogen emission line position assignments given in the first column of table 1 were
Volume 161, number 3
CHEMICAL PHYSICS LETTERS
15 September 1989
Table 1 CzNz fluorescence bands Wavelength &OS (nm)
Absorption frequency kO.01 (cm-‘)
Fluorescence frequency +100 (cm-‘)
Difference frequency + 200 (cm-‘)
218.7 224.0 229.3 230.8 235.0 236.4 242.1 243.1 248.8 250.0 256.4 258.3 263.8 265.0 281.9
45675 [4] 44654 [4]
45717 44642 43599 43322 42550 42308 41297 41033 40186 40005 38994 38720 37909 37136 35469
0 1076 2118 2395 3168 3409 4421 4684 5532 5712 6723 6997 7809 7982 10248
made from spectra that include both Hg resonance lamp lines and cyanogen fluorescence bands. Fig. 3 shows a typical measurement of the total emission intensity measured as a function of time after excitation of the Q branch of the 4; band at 2 18.9 nm. The signal was measured by scanning the 50 nm wide gate of a boxcar analyzer triggered about 200 ns before the laser was fired. The first-order exponential decays were fit by linear regression.
5
* .
4
,,,.,‘,‘,” 0
0 0 2396 0 2334 2302 2288 2364 2303 2303 2313 2277 2269 2267
Lifetimes were measured at seven CzNz pressures between 320 and 29 mTorr. Fig. 4 is a Stern-Volmer plot of the pressure versus measured decay rate. The extrapolated radiative lifetime is 1.34 4 0.09 vs. The collisional quenching rate is (4.36 + 0.15) x 1O-lo cm3/molecule s, which is roughly gas kinetic.
I
0
0 1
2
DECAY TIME (us) Fig. 3. Decay of the emission signal as a function of time after excitation at 218.9 nm. The straight line is the least squares fit whose slope corresponds to a lifetime of 660 ns.
1°304’ nI 2 (cm-‘)
0
1
.
1°3041 I I 0 (cm-‘)
104’ ” 2 (cm-‘)
1°4’ n 0 (cm-‘)
I 100
I
I
200
I
I
300
I
J 400
PRESSURE (mtorr) Fig. 4. Stem-Volmer plot of the decay rate versus CzNz pressure. The extrapolated zero pressure lifetime is 1.34 f 0.07 ps and the quenching rate is (4.36k 0.15) x IO-” cm3/molecule s.
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CHEMICALPHYSICSLETTERS
4. Discussion The first band of the X ‘Z,’ +A ‘C; transition which originates from the lowest vibrational level of the ground state is the 4Aband at 2 18.9 nm [ 41. The symmetry forbidden electronic transition is made allowed by the excitation of one quantum in the v4 nB mode of the excited state. As can be seen in fig. 2, the fluorescence spectrum is very simple, consisting of four- and five-member progressions in the v’~mode of the ground state. The strongest is the 1i4: (n = 0 to 4) progressiofi which has five lines. There are two weaker progressions. The first is the five-member l”, progression starting at the excitation frequency. The second is the 10,394; progression. Finally there is a very weak lz394: progression. Table 1 gives the frequencies of these transitions, and frequency differences within each progression. The first column lists the measured fluorescence wavelength. The second column shows the frequency of those transitions which have also been measured in absorption [4]. The third column indicates the frequency of the fluorescence bands. In the two cases where there are corresponding absorption measurements the emission frequencies agree to well within experimental error. The fourth column states the difference between the excitation frequency and the fluorescence frequency of each line. Columns five through eight list the difference between adjoining members of each progression. The nature of each progression is established by the frequency difference between the exciting line and the first member. For reference, table 2 lists the ground state harmonic frequencies. It should be noted that the frequency difference between 4; and 4: lines is simply the vibrational energy of the ground electronic state 2v4 level. The absorption spectrum seen above the emission Table 2 CzN2ground state frequencies
210
Mode
Frequency (cm- *)
1 2 3 4 5
2329.92 [9] 845.4 141 2157.84 [9] 502.83 [S] 233.72 [IO]
15 September 1989
in fig. 1 has bands at the same line positions as the emission spectrum, but the intensity of the Q branch of the emission spectrum is much larger. The pressure of cyanogen in the cell was 1 Torr and the path length was 68 cm, A UV spectraphotometer (Cary 2390) has been used to measure the absorption spectrum with better signal to noise but at lower resolution (0.04 nm). Based on those measurements the absorption coefficients shown in fig. 1 are reasonable. Starting with the radiative lifetime of 1.34 l.tsone can estimate the transition oscillator strength to be about 5.Ox 10M4.This is about half of the oscillator strength of the OH A 2Z+~X *II transition [ 111. Therefore, if any is present, it should be possible to detect cyanogen emission from objects in the solar system. Using LIF detection an attempt was made to directly measure any photolytic production of CN radical fragments. Tunable light in the 388 nm region was generated by a nitrogen-laser-pumped dye laser. It was possible to detect CN fragments from the photolysis of C2N, using the much weaker 200 nm fourth anti-Stokes beam. However, even though the absorption coefficient is roughly the same as that at 200 nm, there was no detected LIF signal from CN fragments when the 200 nm 4: cyanogen band was scanned. This is a direct confirmation that the dissociation limit is below 218.9 nm [6].
5. Conclusion For the first time singlet emission of cyanogen has been observed. Lines in the excitation spectra match those of the absorption, although the line intensities differ. Frequency intervals of the fluorescence bands correspond to vibrational energy differences of the ground state. The radiative lifetime is 1.34 ps. The strong emission could be used for LIF detection of cyanogen in the laboratory, or for the detection of cyanogen in astronomical objects.
Acknowledgement This work was supported by NASA Grant NAGW785 and by a grant of money from Howard Univer-
Volume I6 I, number 3
CHEMICAL PHYSICS LETTERS
sity. The authors wish to acknowledge many helpful discussions with Dr. Hideo Okabe.
111J.H. Callomon and A.B. Davey, Proc. Phys. Sot. (London) 82 (1963) 335. [2] G.J. Cartwrigth, D.O. O’Hare, A.D. Walshand P.A. Warsop, J. Mol. Spectry. 39 ( 1971) 393. [3 1J.A. Meyer, D.H. Stedman and D.W. Setser, J. Mol. Spectry. 44 (1972)206.
15 September 1989
[4] G.B. Fish, G.J. Cartwright, A.D. Walsh and P.A. Warsop, J. Mol.Spectly.41 (1972)20. [ 51 D.D. Davis and H. Okabe, J. Chem. Phys. 49 (1968) 5526. 161D. Eres, M. Gumick and J.D. McDonald, J. Chem. Phys. 81 (1984) 5552. 173H. Lin, E.A. Johnston and W.M. Jackson, Chem. Phys. Letters 152 (1988) 477. [8] J.A. Russell, LA, McClaren, W.M. Jackson and J.B. Halpern, J. Phys. Chem. 9 1 ( 1987) 3248. [g]A.G.Maki, J. Chem.Phys. 43 (1965) 3193. [ lo] K. Jolma, J. Mol. Spectry. 93 ( 1982) 33. [ 1I] K.R. German, J. Chem. Phys. 63 (1975) 5252.
211
number 3
CHEMICAL PHYSICS LETTERS
15 September 1989
THE EMISSION SPECTRUM OF CZNZ Samuel A. BARTS and Joshua B. HALPERN Department of Chemistry Howard University, Washington. DC 20059. USA Received IS March 1989; in final form 30 June 1989
Cyanogen absorption, excitation and dispersed fluorescence spectra have been measured in the 220 nm region. The radiative lifetime is 1.34 us under collisionless conditions. The fluorescence spectrum following excitation of the 4; band consists of four simple progressions. No CN radical fragments were detected following absorption at 220 nm. This clearly demonstrates the bound nature of the lowest vibrational levels of the A ‘Z; electronic state. The emission could be used for remote detection of cyanogen in astronomical systems.
1. Introduction The 220 nm A ‘E; CX ‘C: transition is the lowest energy singlet absorption of cyanogen. There are two higher wavelength triplet-singlet UV transitions the a 3Zc +-X ‘Zl system at 300 nm [ 1 ] and the b’3A,t X ‘Cl system at 250 nm [ 21. Previously, emission has been observed from the first triplet system [ 31, but there is no report of singlet fluorescence. Fish et al. were able to resolve rotational structure in the bands around 220 nm but not at lower wavelengths [ 41. This suggested that it might be possible to observe the fluorescence spectrum following excitation of the lowest few vibrational levels of the A ‘2;; electronic state. Speaking against this possibility was Davis and Okabe’s bond strength measurement of 5.58kO.05 eV which implies a photodissociation limit of 222.2 &2.0 nm [ 5 1. However, more recently Eres, Gumick and McDonald measured CN radical quantum state distributions after the photolysis of cyanogen at 193 nm [ 61. From the highest measured fragment rotational energy they derived a cyanogen bond energy of 5.83 to.04 eV and a photodissociation limit of 212.7+ 1.3 nm. Lin, Johnston and Jackson have studied the photodissociation of cyanogen at 206 nm using a doubled dye laser as the photolysis source [ 7 1. Based on the last CN rotational state observed they find a bond strength of 5.70 eV and a
dissociation limit of 217.5 nm. They point out that it was possible that a hot band was excited. Thus, 5.70 eV should be regarded as an upper limit and not a lower limit as stated in ref. [ 71. It should be noted that the bandwidth of their photolysis laser was 1.0 cm- ‘, while that of the ArF excimer laser used by Ems, Gumick and McDonald was about 250 cm-‘. Based on Davis and Okabe’s bond strength all lines of the cyanogen X ‘xl +A ‘I;; system will be dissociative [ 51. On the other hand, both Lin et al.‘s and Eres et al.% values for the dissociation limit imply that at least one strong transition, the 4; line at 218.87 nm, terminates in a state that is stable against dissociation. This paper reports measurements of absorption, excitation and dispersed fluorescence spectra of cyanogen in the 220 nm region. The results clearly demonstrate the bound nature of the excited upper state. The fluorescence can be used to detect the formation of cyanogen in astronomical systems such as comets and gas giant planets.
2. Experimental The experimental apparatus has been previously described [ 8 1. The emission spectrum was excited by a frequency-doubled, Nd-YAG-pumped dye laser that was shifted to the 220 nm region by four-wave mixing in 20 atm hydrogen. The third anti-Stokes
0 009-26 14/89/s 03.50 0 Elsevier Science Publishers B.V. ( North-Holland Physics Publishing Division )
207
Volume 161, number 3
15September 1989
CHEMICAL PHYSICS LETTERS
component of the Raman-shifted beams was used to excite the cyanogen. The laser has a bandwidth of 0.4 cm-’ at 600 nm, which results in a resolution of 2.0 cm- ’ or 0.01 nm after doubling and frequency shifting to 220 nm. Fluorescence was observed at right angles to the plane formed by the laser beam and the direction of its electric vector. Total fluorescence was monitored by an eleven-stage EMR VUV photomultiplier. The fluorescence was also dispersed through a 0.25 m Jobin-Yvon monochromator and detected by an eight-stage side-on Hamamatsu photomultiplier tuber. 1.0 and 0.25 mm monochromator slits produced resolutions of 4 and 1 nm in first order, respectively- The intensity of the frequency-shifted exciting light was monitored by a photodiode. The intensity of the light passing through the experimental cell was monitored by a photodiode to yield absorption spectra. Signals were integrated in a PAR model 160 boxcar analyzer. The experiment was controlled by an IBM/XT based data acquisition system designed in our laboratory. The data were recorded by the computer. Cyanogen was bought from the Matheson Co. and purified by freeze-thaw distillation. Cyanogen gas was passed through a vacuum cell at pressures between 1 Torr and 0.5 mTorr as measured by a capacitance manometer.
219.5
219.0
220.0 (nm)
22075
WAVELENGTH
Fig. 1. The excitation spectrum of cyanogen is displayed as a function of exciting light wavelength. The insert above the 4; peak shows the absorbance measured with the same source. The pressure of cyanogen in the cell for the excitation spectrum was 0.01 Torr. The absorption spectrum was measured at 1 Torr.
3. Results Fig. 1 shows the excitation spectrum in the 220 nm region. Only two bands were observed. The total fluorescence was measured while the exciting dye laser was tuned between 2 18 and 222 nm. While fig. 1 displays the total fluorescence as a function of excitation frequency, excitation spectra have also been obtained while monitoring individual fluorescence bands. Such spectra are identical in shape to that seen in fig. 1. The insert above the 4; feature shows the absorption spectrum in this region. Fig. 2 shows the dispersed fluorescence spectrum obtained when the exciting laser is fixed on the Q band head of the 218.9 nm 4; transition. The spectrum was recorded in second orderwith a resolution of 1.0 nm so the resolution of the bands is 0.5 nm. The wavelength scale was calibrated by shining a low 208
210
230
250
WAVELENGTH
270
(nm)
Fig. 2. The fluorescence spectrum of cyanogen excited at 2 18.9 nm on the 4i Q branch (largest feature in the excitation spectrum), The resolution of the scanning monochromator is 0.5 nm in second order. The cyanogen pressure was 0.12 Torr, with the gas passing slowly through the cell. The spectrum consists of four progressions as indicated in the upper part of the figure.
pressure Hg lamp into the experimental cell where a portion was scattered into the monochromator. Cyanogen fluorescence band positions were obtained by interpolation between first- and second-order lines of Hg. The cyanogen emission line position assignments given in the first column of table 1 were
Volume 161, number 3
CHEMICAL PHYSICS LETTERS
15 September 1989
Table 1 CzNz fluorescence bands Wavelength &OS (nm)
Absorption frequency kO.01 (cm-‘)
Fluorescence frequency +100 (cm-‘)
Difference frequency + 200 (cm-‘)
218.7 224.0 229.3 230.8 235.0 236.4 242.1 243.1 248.8 250.0 256.4 258.3 263.8 265.0 281.9
45675 [4] 44654 [4]
45717 44642 43599 43322 42550 42308 41297 41033 40186 40005 38994 38720 37909 37136 35469
0 1076 2118 2395 3168 3409 4421 4684 5532 5712 6723 6997 7809 7982 10248
made from spectra that include both Hg resonance lamp lines and cyanogen fluorescence bands. Fig. 3 shows a typical measurement of the total emission intensity measured as a function of time after excitation of the Q branch of the 4; band at 2 18.9 nm. The signal was measured by scanning the 50 nm wide gate of a boxcar analyzer triggered about 200 ns before the laser was fired. The first-order exponential decays were fit by linear regression.
5
* .
4
,,,.,‘,‘,” 0
0 0 2396 0 2334 2302 2288 2364 2303 2303 2313 2277 2269 2267
Lifetimes were measured at seven CzNz pressures between 320 and 29 mTorr. Fig. 4 is a Stern-Volmer plot of the pressure versus measured decay rate. The extrapolated radiative lifetime is 1.34 4 0.09 vs. The collisional quenching rate is (4.36 + 0.15) x 1O-lo cm3/molecule s, which is roughly gas kinetic.
I
0
0 1
2
DECAY TIME (us) Fig. 3. Decay of the emission signal as a function of time after excitation at 218.9 nm. The straight line is the least squares fit whose slope corresponds to a lifetime of 660 ns.
1°304’ nI 2 (cm-‘)
0
1
.
1°3041 I I 0 (cm-‘)
104’ ” 2 (cm-‘)
1°4’ n 0 (cm-‘)
I 100
I
I
200
I
I
300
I
J 400
PRESSURE (mtorr) Fig. 4. Stem-Volmer plot of the decay rate versus CzNz pressure. The extrapolated zero pressure lifetime is 1.34 f 0.07 ps and the quenching rate is (4.36k 0.15) x IO-” cm3/molecule s.
209
Volume 161, number 3
CHEMICALPHYSICSLETTERS
4. Discussion The first band of the X ‘Z,’ +A ‘C; transition which originates from the lowest vibrational level of the ground state is the 4Aband at 2 18.9 nm [ 41. The symmetry forbidden electronic transition is made allowed by the excitation of one quantum in the v4 nB mode of the excited state. As can be seen in fig. 2, the fluorescence spectrum is very simple, consisting of four- and five-member progressions in the v’~mode of the ground state. The strongest is the 1i4: (n = 0 to 4) progressiofi which has five lines. There are two weaker progressions. The first is the five-member l”, progression starting at the excitation frequency. The second is the 10,394; progression. Finally there is a very weak lz394: progression. Table 1 gives the frequencies of these transitions, and frequency differences within each progression. The first column lists the measured fluorescence wavelength. The second column shows the frequency of those transitions which have also been measured in absorption [4]. The third column indicates the frequency of the fluorescence bands. In the two cases where there are corresponding absorption measurements the emission frequencies agree to well within experimental error. The fourth column states the difference between the excitation frequency and the fluorescence frequency of each line. Columns five through eight list the difference between adjoining members of each progression. The nature of each progression is established by the frequency difference between the exciting line and the first member. For reference, table 2 lists the ground state harmonic frequencies. It should be noted that the frequency difference between 4; and 4: lines is simply the vibrational energy of the ground electronic state 2v4 level. The absorption spectrum seen above the emission Table 2 CzN2ground state frequencies
210
Mode
Frequency (cm- *)
1 2 3 4 5
2329.92 [9] 845.4 141 2157.84 [9] 502.83 [S] 233.72 [IO]
15 September 1989
in fig. 1 has bands at the same line positions as the emission spectrum, but the intensity of the Q branch of the emission spectrum is much larger. The pressure of cyanogen in the cell was 1 Torr and the path length was 68 cm, A UV spectraphotometer (Cary 2390) has been used to measure the absorption spectrum with better signal to noise but at lower resolution (0.04 nm). Based on those measurements the absorption coefficients shown in fig. 1 are reasonable. Starting with the radiative lifetime of 1.34 l.tsone can estimate the transition oscillator strength to be about 5.Ox 10M4.This is about half of the oscillator strength of the OH A 2Z+~X *II transition [ 111. Therefore, if any is present, it should be possible to detect cyanogen emission from objects in the solar system. Using LIF detection an attempt was made to directly measure any photolytic production of CN radical fragments. Tunable light in the 388 nm region was generated by a nitrogen-laser-pumped dye laser. It was possible to detect CN fragments from the photolysis of C2N, using the much weaker 200 nm fourth anti-Stokes beam. However, even though the absorption coefficient is roughly the same as that at 200 nm, there was no detected LIF signal from CN fragments when the 200 nm 4: cyanogen band was scanned. This is a direct confirmation that the dissociation limit is below 218.9 nm [6].
5. Conclusion For the first time singlet emission of cyanogen has been observed. Lines in the excitation spectra match those of the absorption, although the line intensities differ. Frequency intervals of the fluorescence bands correspond to vibrational energy differences of the ground state. The radiative lifetime is 1.34 ps. The strong emission could be used for LIF detection of cyanogen in the laboratory, or for the detection of cyanogen in astronomical objects.
Acknowledgement This work was supported by NASA Grant NAGW785 and by a grant of money from Howard Univer-
Volume I6 I, number 3
CHEMICAL PHYSICS LETTERS
sity. The authors wish to acknowledge many helpful discussions with Dr. Hideo Okabe.
111J.H. Callomon and A.B. Davey, Proc. Phys. Sot. (London) 82 (1963) 335. [2] G.J. Cartwrigth, D.O. O’Hare, A.D. Walshand P.A. Warsop, J. Mol. Spectry. 39 ( 1971) 393. [3 1J.A. Meyer, D.H. Stedman and D.W. Setser, J. Mol. Spectry. 44 (1972)206.
15 September 1989
[4] G.B. Fish, G.J. Cartwright, A.D. Walsh and P.A. Warsop, J. Mol.Spectly.41 (1972)20. [ 51 D.D. Davis and H. Okabe, J. Chem. Phys. 49 (1968) 5526. 161D. Eres, M. Gumick and J.D. McDonald, J. Chem. Phys. 81 (1984) 5552. 173H. Lin, E.A. Johnston and W.M. Jackson, Chem. Phys. Letters 152 (1988) 477. [8] J.A. Russell, LA, McClaren, W.M. Jackson and J.B. Halpern, J. Phys. Chem. 9 1 ( 1987) 3248. [g]A.G.Maki, J. Chem.Phys. 43 (1965) 3193. [ lo] K. Jolma, J. Mol. Spectry. 93 ( 1982) 33. [ 1I] K.R. German, J. Chem. Phys. 63 (1975) 5252.
211