- Email: [email protected]
Infrared spectrum and molecular constants of gaseous tritium fluoride
JOURNAL
OF
MOLECULAR
SPECTROSCOPY
1,
43-48 (1957)
Infrared Spectrum and Molecular Constants of Gaseous Tritium Fluoride’ LLEWELLYNH. JONES AND Los Alamos
ScientiJic Laboratory,
MAXWELL GOLDBLATT
Cmiversily of California,
Los Alamos,
New Mexico
The vibration-rotation lines of Y,+Oand YZ+Ofor tritium fluoride (g) have been observed with =l cm-l and ~2.5 cm-1 resolution, respectively. Molecular constants were calculated from the observed frequencies. Within the accuracy of measurement the observed constants agree with those previously reported (1) for hydrogen fluoride (g). The “least squares” values of t,he molecular constants in cm-‘are: Y,~,, = 2443.86, Y~+O= 4823.8, w, = 2508.5, x,w, = 32.5, B, = 7.69 , a, = 0.176, D, = 2.5 X lo@. The bond distance is 0.917 A and the force constant is 9.65 X lo6 dynes/cm. INTRODUCT
The molecular constants of gaseous HF were recently reported by Kuipers, Smith, and Nielsen (1). Reference 1 gives a discussion of earlier work. We have observed the fundamental and first overtone spectrum of TF under medium high resolution and have calculated molecular constants for comparison with values calculated from those of HF.
PREPARATIONOF TF About 20 cc (STP) of tritium fluoride were made by reduction of silver difluoride with tritium gas at 100°C. The TF was separated from the unreacted Tz by condensing the TF with liquid nitrogen in a trap connected to the infrared cell and then pumping off the tritium through the trap. The cell and the connecting trap were bhen sealed off with monel valves and the TF was allowed to expand into the cell. SPECTROMETER The spectrometer used is a Perkin-Elmer Model 112 with a lithium fluoride prism and with the Littrow mirror replaced by a 300 groove/mm Bausch and Lomb “CP” grating. The source was a globar. The detectors were a thermo1This work was sponsored
by the U. S. Atomic Energy .t3
Commission
44
JONES AND GOLDBLATT
couple in the 4 micron region and a lead sulfide cell in the 2 micron region. From the observed half-width of the TF lines we estimate resolution of ~1 cm-’ in the 2200-2700 cm-’ region and of ~2.5 cm-’ in the 4600-5000 cm-’ region. ABSORPTIONCELL The TF was cont,ained in a lo-cm cell made of monel with a copper insert to decrease the volume without restricting the light path. The insert was of rectangular aperture, tapered to the convergence of the light beam. Calcium fluoride windows were pressed against teflon gaskets coated with halocarbon grease for a vacuum seal.
c
PATH FIQ. 1. Vibration-rotation
=
IOcm.
fundamental
of TF.
INFRAREDSPECTRUMOF TRITIUM FLUORIDE
45
CALIBRATIONOF SPECTROMETER In the region of the fundamental the spectrometer was calibrated with the gases HBr (2), COZ (3), and CO (4). The first overtone region was calibrated with a few H&3 lines (5), a helium emission line (6) at 4857.55 cm-‘, and a krypton emission line (7) at 4564.45 cm-‘. For both regions a Friedel-McKinney equation (8) was derived to fit the calibration standards and then used to calculate the TF frequencies. RESULTS The vibration-rotation bands of the fundamental shown in Figs. 1 and 2, respectively. I
I
4800
4850
-
and first overtone of TF are I
4900cm-’
TF PRESSURE
GAS = 24cm = IO cm
PATH
Hg
P P,
P,
P,
\ I
P6
k
p5
P4 %
**
4650
4700
I of TF first overtone FIG. 2. Vibration-rotation
4750cm-’
46
JONES
AND
GOLDBLATT
The molecular constants were calculated to obtain the observed frequencies with the usual expression
I
RJ-1 P,
=
V”4l
f
a “least
squares”
fit of
(Bo + B,)J + [(B” - Bo) - (a - Do)lJ2 =F 2(DV + D&I3
-
(DV -
D&I*.
For HF it was found (I) necessary to include terms in 5’ and J6 for the best fit. However, the data presented here are not sufficiently accurate to warrant such terms, which make a difference of only 0.05 cm-’ in the highest J values observed. From D, , Do , B, , and Bo , CY,, ye , be , B, , and D, were calculated using the relations & = B, 0, The vibrational However, Kuipers
4~
+ 3) + re(v + 3)‘,
= D, + P&J + 9.
constants, we and W,X, , were calculated from vltO and yzco . and co-workers (I) found it necessary to include cubic and TABLE
I
MOLECULAR CONSTANTS FOR TF
Constant
Observed
2443.86 4823.8
f f
0.04 cm-l 0.11
2508.54 32.54
f f
0.23 0.10 -
f f f f i f f f f f f f f * zt f
0.0142 0.0047 0.0047 0.0142 0.008 0.011 0.0103 0.0044 1.8 x 0.3 X 0.3 X 1.8 X 7.3 x 5.3 x 0.0005A 0.0018
2.9 2.7 2.6 2.5 9 4
a Limits
in this investigation”
7.2663 7.4306 7.6025 7.6063 7.690 7.694 0.1757 0.0019 x IO-4 X 10-d X lo+ X 1OP x 10-s X 10-S 0.917 9.6492
given are 9570 confidence
limits.
10-d 1OP lo+ 1OP 10-G 10-b X lo6 dynes/cm
Calculated from those of HF (ref./)
2443.87 4823.7 2508.73 32.62 0.1189 -0.0029 7.2692 7.4404 7.6139 7.6139 7.7015 7.7015 0.1759 0.0012 2.80 X 1OP 2.84 X 1OP 2.87 X 1OP 2.87 X 1OP -3 x 10-e -3 x 10-S 0.9170 9.6507
INFRARED
SPECTRUM
OF TRITIUM
TABLE VIBRATION-ROTATION Yl_“,
LINES OF TF vzco,
Obs-Calc
2626.64 2617.37 2607.65 2597.48 2586.88 2575.85 2564.40 2552.54 2540.28
-0.13 0.06 0.10 -0.02 0.08 -0.08 0.04 -0.10
2397.24 2381.04 2364.52 2347.69 2330.54 2313.10 2295.35 2277.30 2258.97 2240.35 2221.44 2202.26
II
cm-’
CdC
2527.62 2514.59 2501.17 2487.38 2473.23 2458.72 2428.65 2413.11
47
FLUORIDE
CdC
cm-1 Obs-Calr
0.01
0.05 -0.02 -0.07 0.02 -0.05 0.08 -0.03 -0.04 -0.05 0.02 0.16 -0.02 0.03 0.01 0.00 -0.02
4944.2 4937.0 4929. I 4920.3 4910.8 4900.5 4889.5 4877.8 4865.3 4852.2 4838.3 4808.6 4792.7 4776.1 4758.9 4741 .o 4722.5 4703.3 4683.4 4663.9 4641.7
0.3 -0.1 0.0 0.1 0.0 0.2 0.0 0.0 0.0 -0.1 0.0 0.0 0.0 0.0 -0.1 0.1 -0.2 0.1 -0.1 -0.1 0.0
-0.05 -0.08 -0.03 0.10
quartic terms. Therefore, values of (LICIT and w,xF were calculated for TF and included for determination of we and W,X, . The resulting molecular constants are listed in Table I along with those calculated from the constants given in Ref. I and the mass dependence relationships (9). Using the values given in column 2 of Table I, the vibration-rotation frequencies were calculated for y14 and v2+_0of TF. Table II gives the calculated values and the deviation of the observed values. In general the agreement of observed constants with those calculated from HF is good. The observed values of B1 , Bo , and B, are slightly low. However, the discrepancy cannot be considered as significant), as the value found for &
48
JONES AND GOLDBLATT
is too large and of the wrong sign. The theoretical expressions for D, and Pe found in Ref. 9 (pp. 107-108) yield 2.9 X lop4 and -5 X 10h6, respectively. Part of the error may be ascribed to overlapping of some of the TF lines by COr lines causing slight displacements. The instrument was swept continuously with argon, but the CO2 peaks did not disappear completely, as seen in Fig. 1. Perhaps an equal source of error is the application of the Friedel-McKinney equation for calibration in the region between the COz lines and the CO lines. If we calculate the frequencies of the vibration-rotation lines of vltO for TF, using the constants in the last column of Table I, the agreement is good. The only lines off by more than 0.2 cm-’ are RI4 , RI3 , and Ps ( vobs- scale= - 0.35, -0.41, and +0.28 cm-‘), respectively. RI4 and RI3 are quite weak and perhaps should be excluded. Pg is seriously overlapped by a CO* peak. ACKNOWLEDGMENTS The authors are grateful to Mr. Dale Armstrong for preparation of the figures, to Mr. Keith Zeigler for the least squares treatment of the data, and to Miss Suzanne Krainock for some of the measurements and calculations. RECEIVED:
February
16, 1957 REFERENCES
1. G. A. KUIPERS, D. F. SMITH, AND A. H. NIELSEN, .I. Chem. Phys. 26,275 (1956). d. H. W. THOMPSON, R. L. WILLIAMS, AND H. J. CALLOMAN, Spectrochim. Acta 6,313 2. 4. 6. 6. 7.
A. E. H. C. E.
(1952).
H. NIELSEN AND Y. T. YAO, Phys. Reu. 68, 173 (1945); 71, 825 (1947). K. PLYLER, L. R. BLAINE, AND W. S. CONNOR, J. Opt. Sot. Am. 46, 102 (1955). C. ALLEN, JR., AND E. K. PLYLER, J. Chem. Phys. 22, 1104 (1954). J. HUMPHREYS AND H. J. KOSTXOWSKI, J. Research Natl. Eur. Standards 49,73 (1952). K. PLYLER, L. R. BLAINE, AND E. D. TIDWELL, J. Research Natl. Bur. Standards 66,
279 (1955).
8. D. S. MCKINNEY AND R. A. FRIEDEL, J. Opt. Sot. Am. 38, 222 (1948). 9. G. HERZBERG, “Spectra New Jersey, 1950.
of Diatomic
Molecules,”
pp. 141-145. Van Nostrand,
Princeton,
OF
MOLECULAR
SPECTROSCOPY
1,
43-48 (1957)
Infrared Spectrum and Molecular Constants of Gaseous Tritium Fluoride’ LLEWELLYNH. JONES AND Los Alamos
ScientiJic Laboratory,
MAXWELL GOLDBLATT
Cmiversily of California,
Los Alamos,
New Mexico
The vibration-rotation lines of Y,+Oand YZ+Ofor tritium fluoride (g) have been observed with =l cm-l and ~2.5 cm-1 resolution, respectively. Molecular constants were calculated from the observed frequencies. Within the accuracy of measurement the observed constants agree with those previously reported (1) for hydrogen fluoride (g). The “least squares” values of t,he molecular constants in cm-‘are: Y,~,, = 2443.86, Y~+O= 4823.8, w, = 2508.5, x,w, = 32.5, B, = 7.69 , a, = 0.176, D, = 2.5 X lo@. The bond distance is 0.917 A and the force constant is 9.65 X lo6 dynes/cm. INTRODUCT
The molecular constants of gaseous HF were recently reported by Kuipers, Smith, and Nielsen (1). Reference 1 gives a discussion of earlier work. We have observed the fundamental and first overtone spectrum of TF under medium high resolution and have calculated molecular constants for comparison with values calculated from those of HF.
PREPARATIONOF TF About 20 cc (STP) of tritium fluoride were made by reduction of silver difluoride with tritium gas at 100°C. The TF was separated from the unreacted Tz by condensing the TF with liquid nitrogen in a trap connected to the infrared cell and then pumping off the tritium through the trap. The cell and the connecting trap were bhen sealed off with monel valves and the TF was allowed to expand into the cell. SPECTROMETER The spectrometer used is a Perkin-Elmer Model 112 with a lithium fluoride prism and with the Littrow mirror replaced by a 300 groove/mm Bausch and Lomb “CP” grating. The source was a globar. The detectors were a thermo1This work was sponsored
by the U. S. Atomic Energy .t3
Commission
44
JONES AND GOLDBLATT
couple in the 4 micron region and a lead sulfide cell in the 2 micron region. From the observed half-width of the TF lines we estimate resolution of ~1 cm-’ in the 2200-2700 cm-’ region and of ~2.5 cm-’ in the 4600-5000 cm-’ region. ABSORPTIONCELL The TF was cont,ained in a lo-cm cell made of monel with a copper insert to decrease the volume without restricting the light path. The insert was of rectangular aperture, tapered to the convergence of the light beam. Calcium fluoride windows were pressed against teflon gaskets coated with halocarbon grease for a vacuum seal.
c
PATH FIQ. 1. Vibration-rotation
=
IOcm.
fundamental
of TF.
INFRAREDSPECTRUMOF TRITIUM FLUORIDE
45
CALIBRATIONOF SPECTROMETER In the region of the fundamental the spectrometer was calibrated with the gases HBr (2), COZ (3), and CO (4). The first overtone region was calibrated with a few H&3 lines (5), a helium emission line (6) at 4857.55 cm-‘, and a krypton emission line (7) at 4564.45 cm-‘. For both regions a Friedel-McKinney equation (8) was derived to fit the calibration standards and then used to calculate the TF frequencies. RESULTS The vibration-rotation bands of the fundamental shown in Figs. 1 and 2, respectively. I
I
4800
4850
-
and first overtone of TF are I
4900cm-’
TF PRESSURE
GAS = 24cm = IO cm
PATH
Hg
P P,
P,
P,
\ I
P6
k
p5
P4 %
**
4650
4700
I of TF first overtone FIG. 2. Vibration-rotation
4750cm-’
46
JONES
AND
GOLDBLATT
The molecular constants were calculated to obtain the observed frequencies with the usual expression
I
RJ-1 P,
=
V”4l
f
a “least
squares”
fit of
(Bo + B,)J + [(B” - Bo) - (a - Do)lJ2 =F 2(DV + D&I3
-
(DV -
D&I*.
For HF it was found (I) necessary to include terms in 5’ and J6 for the best fit. However, the data presented here are not sufficiently accurate to warrant such terms, which make a difference of only 0.05 cm-’ in the highest J values observed. From D, , Do , B, , and Bo , CY,, ye , be , B, , and D, were calculated using the relations & = B, 0, The vibrational However, Kuipers
4~
+ 3) + re(v + 3)‘,
= D, + P&J + 9.
constants, we and W,X, , were calculated from vltO and yzco . and co-workers (I) found it necessary to include cubic and TABLE
I
MOLECULAR CONSTANTS FOR TF
Constant
Observed
2443.86 4823.8
f f
0.04 cm-l 0.11
2508.54 32.54
f f
0.23 0.10 -
f f f f i f f f f f f f f * zt f
0.0142 0.0047 0.0047 0.0142 0.008 0.011 0.0103 0.0044 1.8 x 0.3 X 0.3 X 1.8 X 7.3 x 5.3 x 0.0005A 0.0018
2.9 2.7 2.6 2.5 9 4
a Limits
in this investigation”
7.2663 7.4306 7.6025 7.6063 7.690 7.694 0.1757 0.0019 x IO-4 X 10-d X lo+ X 1OP x 10-s X 10-S 0.917 9.6492
given are 9570 confidence
limits.
10-d 1OP lo+ 1OP 10-G 10-b X lo6 dynes/cm
Calculated from those of HF (ref./)
2443.87 4823.7 2508.73 32.62 0.1189 -0.0029 7.2692 7.4404 7.6139 7.6139 7.7015 7.7015 0.1759 0.0012 2.80 X 1OP 2.84 X 1OP 2.87 X 1OP 2.87 X 1OP -3 x 10-e -3 x 10-S 0.9170 9.6507
INFRARED
SPECTRUM
OF TRITIUM
TABLE VIBRATION-ROTATION Yl_“,
LINES OF TF vzco,
Obs-Calc
2626.64 2617.37 2607.65 2597.48 2586.88 2575.85 2564.40 2552.54 2540.28
-0.13 0.06 0.10 -0.02 0.08 -0.08 0.04 -0.10
2397.24 2381.04 2364.52 2347.69 2330.54 2313.10 2295.35 2277.30 2258.97 2240.35 2221.44 2202.26
II
cm-’
CdC
2527.62 2514.59 2501.17 2487.38 2473.23 2458.72 2428.65 2413.11
47
FLUORIDE
CdC
cm-1 Obs-Calr
0.01
0.05 -0.02 -0.07 0.02 -0.05 0.08 -0.03 -0.04 -0.05 0.02 0.16 -0.02 0.03 0.01 0.00 -0.02
4944.2 4937.0 4929. I 4920.3 4910.8 4900.5 4889.5 4877.8 4865.3 4852.2 4838.3 4808.6 4792.7 4776.1 4758.9 4741 .o 4722.5 4703.3 4683.4 4663.9 4641.7
0.3 -0.1 0.0 0.1 0.0 0.2 0.0 0.0 0.0 -0.1 0.0 0.0 0.0 0.0 -0.1 0.1 -0.2 0.1 -0.1 -0.1 0.0
-0.05 -0.08 -0.03 0.10
quartic terms. Therefore, values of (LICIT and w,xF were calculated for TF and included for determination of we and W,X, . The resulting molecular constants are listed in Table I along with those calculated from the constants given in Ref. I and the mass dependence relationships (9). Using the values given in column 2 of Table I, the vibration-rotation frequencies were calculated for y14 and v2+_0of TF. Table II gives the calculated values and the deviation of the observed values. In general the agreement of observed constants with those calculated from HF is good. The observed values of B1 , Bo , and B, are slightly low. However, the discrepancy cannot be considered as significant), as the value found for &
48
JONES AND GOLDBLATT
is too large and of the wrong sign. The theoretical expressions for D, and Pe found in Ref. 9 (pp. 107-108) yield 2.9 X lop4 and -5 X 10h6, respectively. Part of the error may be ascribed to overlapping of some of the TF lines by COr lines causing slight displacements. The instrument was swept continuously with argon, but the CO2 peaks did not disappear completely, as seen in Fig. 1. Perhaps an equal source of error is the application of the Friedel-McKinney equation for calibration in the region between the COz lines and the CO lines. If we calculate the frequencies of the vibration-rotation lines of vltO for TF, using the constants in the last column of Table I, the agreement is good. The only lines off by more than 0.2 cm-’ are RI4 , RI3 , and Ps ( vobs- scale= - 0.35, -0.41, and +0.28 cm-‘), respectively. RI4 and RI3 are quite weak and perhaps should be excluded. Pg is seriously overlapped by a CO* peak. ACKNOWLEDGMENTS The authors are grateful to Mr. Dale Armstrong for preparation of the figures, to Mr. Keith Zeigler for the least squares treatment of the data, and to Miss Suzanne Krainock for some of the measurements and calculations. RECEIVED:
February
16, 1957 REFERENCES
1. G. A. KUIPERS, D. F. SMITH, AND A. H. NIELSEN, .I. Chem. Phys. 26,275 (1956). d. H. W. THOMPSON, R. L. WILLIAMS, AND H. J. CALLOMAN, Spectrochim. Acta 6,313 2. 4. 6. 6. 7.
A. E. H. C. E.
(1952).
H. NIELSEN AND Y. T. YAO, Phys. Reu. 68, 173 (1945); 71, 825 (1947). K. PLYLER, L. R. BLAINE, AND W. S. CONNOR, J. Opt. Sot. Am. 46, 102 (1955). C. ALLEN, JR., AND E. K. PLYLER, J. Chem. Phys. 22, 1104 (1954). J. HUMPHREYS AND H. J. KOSTXOWSKI, J. Research Natl. Eur. Standards 49,73 (1952). K. PLYLER, L. R. BLAINE, AND E. D. TIDWELL, J. Research Natl. Bur. Standards 66,
279 (1955).
8. D. S. MCKINNEY AND R. A. FRIEDEL, J. Opt. Sot. Am. 38, 222 (1948). 9. G. HERZBERG, “Spectra New Jersey, 1950.
of Diatomic
Molecules,”
pp. 141-145. Van Nostrand,
Princeton,