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Infrared-microwave double resonance as an aid in assignment of optically pumped submillimetre laser lines: CH2CF2, CH2F2, and CH3OH
JOURNAL OF MOLECULAR
SPECI-ROSCOPY
100,396-402(1983)
Infrared-Microwave Double Resonance as an Aid in Assignment of Optically Pumped Submillimetre Laser Lines: CH&F2, CH2F2, and CH30H J. C. PETERSEN,’
D. IGNER,’
AND G. DUXBURY
Department of Natural Philosophy, University of Strathciyde. 107 Rottenrow, Glasgow G4 ONG. Scotland
Infrared-microwave double resonance has been used to confirm recent assignments of optically pumped submillimeter wave laser lines in CH&F, and CHsOH, as well as a tentative assignment of a line in CF2Hz. Intracavity double resonance signals have also been obtained in CF2CH2 using a circular copper waveguide laser. INTRODUCTION
The assignment of optically pumped laser lines and their parent pump lines is of considerable importance in the modeling of laser behavior. One particular technique which is suitable for this purpose is infrared-microwave double resonance. This is now a well-established technique for spectroscopic studies, both of the ground state and of vibrationally excited states, of molecules absorbing in the infrared. Recently the technique has been used to confirm assignments of submillimeter laser lines in CH30H (I, 2) and to support the existence of an x state close to the C-O stretching state in CH30H (3) postulated by Henningsen (4). Assignments made in this way are particularly important in molecules such as CH30H and CF*Hz, where the excited states are not particularly well characterized. We have recently observed many new optically pumped submillimeterwave laser lines in CHzCFz (5), CHzFz (6), and CH30H (7) using isotopically labeled CO2 lasers. Many of these lines were assigned using primarily wavelength data, and we can now confirm some of these assignments owing to the observation of IRMWDR signals on connected transitions. IRMWDR has not previously been reported to CHzCFz, although signals were observed in CHIFz in the presence of a Stark field (8). Intracavity double resonance experiments to study the active medium of a submillimeter laser were first carried out by a Dangoisse et al. (9, IO) using an open resonator. Arimondo et al. (II) used a similar method to confirm an assignment in CH30H by introducing rf power into a dielectric waveguide. The use of a circular copper waveguide laser in the present experiments increases the microwave power density, and hence a larger effect is expected. Double resonance signals were observed on several submillimeter transitions using three different microwave pumping transitions. ’ present address: Hemberg Institute of Astrophysics, National Research Council Canada, Ottawa, Canada. ’ Formerly of Dept. of Theoretical Chemistry, Bristol University. 0022-2852183 $3.00 Copyright 0 1983 by Academic Press. Inc. All rights of reprcduction in any form resewed.
396
LASER
LINES
OF CH2CF2,
EXPERIMENTAL
CH2F2,
and
CHIOH
397
APPARATUS
In the experiment an extracavity K-band absorption cell was used. The cell was 1.4 m long and terminated at each end by KC1 Brewster windows. The CO2 beam was focused into the cell using two ZnSe lenses and after a double pass the infrared beam was monitored using a PbSnTe detector. The double resonance effect was detected as a change in infrared absorption when the microwave frequency was tuned. The microwave region from 21 to 32 GHz was covered using three high power klystrons (OIU 24V11, 20’12, 3OV12). The microwave power was introduced into the cell via a K-band waveguide mounted perpendicular to the absorption cell. The microwave frequency was modulated at 5 kHz and a voltage ramp was used for scanning the microwave frequency over 150 MHz. The resulting absorption signals were observed using phase-sensitive detection. Parallel polarization of the microwave and infrared fields was used. The frequencies were measured by monitoring beats between the klystron frequency and a Micro-Now frequency multiplication chain, using a radio receiver. The accuracy of the measurements is estimated to *OS MHz. To obtain double-resonance signals within a submillimeter laser cavity a circular copper waveguide laser was used, and the microwaves introduced via a K-band waveguide mounted perpendicular to the tube near one of the mirrors. The submillimeter laser was held tuned to the power peak of the transition being studied while the microwave frequency was slowly swept. The change in the output power of the laser was monitored with a Golay cell detector. OBSERVED
DOUBLE
RESONANCE
SIGNALS
The search for double resonance signals in the three asymmetric top molecules CH2CF2, CHzFz, and CH30H was mainly concentrated on CO2 laser lines where opto-acoustic signals had been observed (22) and corresponding optically pumped submillimeter laser lines had been found.
The CHzCFz molecule has been extensively studied using laser Stark (13) and diode laser spectroscopy (14). In Ref. (24) molecular constants for the u4 (CF2 symm stretch) and u9 (CHz in-plane rocking) vibrational bands have been determined with great accuracy and it has therefore been possible to assign most submillimeter laser lines from the CH2CF2 molecule. The double resonance signals observed in CFzCHz therefore, beside confirming existing assignments, also enable a comparison of the frequency of observed excited state microwave transitions with those calculated using the constants deduced previously (13, 14). Three double resonance signals were observed using CO;? laser lines which are known to act as pump lines for submillimeter laser action. The frequencies and assignments are given in Table I. Two strong double resonance signals were observed when using the ‘3C’602 1OR(14) laser line, which were known to act as a pump for submillimeter emission lines (5). The microwave transitions were assigned using the rotational constants determined by Lafferty et al. (14). The microwave, submillimeter, and infrared transitions are shown in Fig. 1. The infrared absorption transition is a parallel transition in the Q branch of the v4 band. The microwave transitions are K-doublet transitions in the
398
PETERSEN, INGER, AND DLJXBURY TABLE I Assigned Infrared-Microwave Double Resonances in CH2CF2 Observed frequency (MHZ)
Microwave transition
o-c (MHz)
Infrared
transition
"* state (27 22 5) - (27 22 6)
0.0
23363.4
(27 22 6) - (27 22 5) 9.s. (27 22 5) -
vg
(27 22 6)
2
21688=
state
(20 16 4) - (20 16 5)
a - Klystron
operatinq
-0.3
25652.9
at
its
low
frequency
limit and the
(20 16 4) - (20 17 3)
beats
were
unstable.
ground and u4 states. Both share a common level with the infrared transition. A very strong double resonance was observed using the i2Ci602 lOP( 10) laser line. The transition can be assigned to a v9 state K-doublet transition (20 16 4)-(20 16 5), and confirms the assignment of the submillimeter laser line observed using this CO2 pump line. The transitions are shown in Fig. 2. The three microwave transitions were also found to have influence on the output power of the submillimeter waveguide laser when introduced into the cavity. A typical signal is shown in Fig. 3. The ~-MHZ linewidth (FWHM) of the signal is produced mainly by pressure broadening. The signal shown corresponds to the microwave transition shown in Fig. 2. The resonance appears as a sharp decrease in the submillimeter laser power. This can be explained by a change in population. The population in the u9 state is very low at room temperature and the main population here is transferred into level 20L6,4by the CO2 pump laser. The population of this level is depleted by the microwave transition, thus reducing the population inversion responsible for the submillimeter laser oscillation. The 23 363.4-MHz microwave transition in the scheme shown in Fig. 1 caused a decrease in the laser power output while the 2 1 688-MHz microwave transition caused an increase in power. In the latter case the infrared pumping removes a noticeable number of molecules from level 2722,5in the ground state. The high power microwave radiation will try to equalize the populations of the levels 27 22,5and 2722,6in the ground state and more molecules are available for pumping by the laser, leading to an increase in the submillimeter laser power.
The methylene fluoride molecule has been shown to be one of the most efficient submillimeter wave laser molecules in the short wavelength region below 300 pm (15, 16). Tentative assignments of laser lines from this molecule have only recently been made (6). Although the main infrared absorption of the CO2 laser power is expected to be associated with transitions in the v9 (CF2 asym stretch) and the v3 (CF symm stretch)
LASER
LINES
OF CH2CF2, CH2F2, and CH,OH
399
27 22 5
23363.4MHz
27 22 6
26 26
22 4 22 5
FIG. I. Energy level diagram showing the microwave, CH2CF2 using the ‘3C’602 lOR( 14) laser line.
submillimeter
laser, and infrared transitions
in
bands, at 1090.1 and 1113.2 cm-‘, respectively, some absorption may be due to hot band transitions, since the frequency of the v4 band is very low at 528.5 cm-‘. These possibilities, together with strong Coriolis coupling between the u9 and v3 vibrational states, complicate the process of assignment. A very strong double resonance was observed when using the 9R(34) ‘%?OZ laser line. We have previously observed a submillimeter laser line using this pump line and given a tentative assignment for the submillimeter and infrared transitions involved (6). The microwave transition at 23 864.8 MHz had previously been observed and assigned by Lide (17). Its assignment, to the ground state transition (32 8 24) - (3 1 9 23), confkns the previous assignments. All transitions involved are shown in Fig. 4. The microwave transition was calculated using the molecular constants given by Hirota (18). The difference between the cal20 20
19
164 16 5
256529
MHz
164
FIG. 2. Schematic diagram of the energy levels of the VPband of CH,CFz involved in the double resonance experiment.
400
PETERSEN,
INGER,
AND
DUXBURY
MHz
25653
FIG. 3. Change of SMMW laser output power with microwave pump frequency. The laser was tuned to the top of its mode profile. The microwave transition is the 20,6A - 2016,5 transition in the vs state of CHrCFr. The SMMW emission transition is 20,6,4 - 19r6,r. The pressure was ca. 100 mTorr.
culated and measured value for the transition is 2.0 MHz. This is partly due to the fact that the rotational constants were derived from transitions with J d 20 and K, =S6 (18). The transition (33 8 25)-(33 7 26) in the u9 state is a potential laser transition, with a calculated wavelength of 535.4 pm. CH30H This molecule is one of the most studied submillimeter laser gases, and accounts for more than 200 laser lines (4), but its spectrum is still not completely understood. This is partly due to the complexity of the hindered internal rotation of the hydroxyl group with respect to the methyl group and its interaction with other vibrational modes. Any additional information on the spectrum is therefore very important. A double resonance signal was observed when using the ‘2C’802 9P( 16) pump line. This line has previously been used for generation of three very strong submillimeter laser lines, all of which could be assigned (7). These lines together with the microwave transition are shown in Fig. 5. The microwave transition was measured to be 30 189.8 MHz, and could be assigned to the (017, 27)-(038, 26) ground state transition, using calculations based on the molecular constants and Hamiltonian of Kwan and Dennison (I 9). 33 825 33 826
T
“C ‘q
LASER
9Rl341
Rc. 4. Energy level scheme for the (33 8 25) - (32 8 24) transition of CHrFr of the v9 band probed by the 9R(34) ‘2C’802 laser line. The submillimeter wave laser transition is shown in the excited state, and the microwave pump transition in the ground state. K-doublet splittings are not to scale.
LASER LINES OF CH2CF2, CHzFz, and CHsOH
401
28 27
44.61 cti’
“C”Q
i
026
017
LASER 9Pil6)
038
flTK
FIG. 5. Energylevel scheme for the QR(O17,27) transitionof CH3OH pumped by the 9P(16) ‘*C’*O2 laserline. FIR transitionsare shown in the excited state and the microwave probe transition is shown in the ground state.
CONCLUSION
We have observed several double resonance signals in CH2CF2, CH2F2, and CH30H which have all confirmed our original assignments of optically pumped submillimeter laser lines. Several other double resonance signals which could not be associated with submillimeter laser action were observed in the region 2 l-32 GHz. These comprise four double-resonance signals in CH2CF2 and four signals in CHzFz . Analysis of these is in progress. RECEIVED: April
5,
1983 REFERENCES
I. 2. 3. 4.
R. M. LEES,C. YOUNG, J. VAN DERLINDE,AND B. A. OLIVER,J. Mol. Spectrosc.75, 161-167 (1979). C. YOUNG, R. M. LEES,J. VAN DERLINDE,AND B. A. OLIVER,J. Appl. Phys. 50, 3808-38 10 (1979). R. M. LEES,M. A. WALTON,AND J. 0. HENNINGSEN, J. Mol. Spectrosc. 88, 90-94 (I 98 I). J. 0. HENNINGSEN, J. Mol. Spectrosc. 83, 70-93 (1980).
402
PETERSEN,
INGER,
AND DUXBURY
5. J. M~COMBIE,J. C. PETERSEN, AND G. DUXBURY, in “Quantum Electronicsand Electra-Optics,” (P. L. Knight, Ed.), pp. 251-253, Wiley, New York, 1983. 6. J. C. PETERSEN AND G. DUXBURY,ht. J. IR and Mm Waves 3, 607-618 (1982). 7. J. C. PETERSEN ANLIG. DUXBURY,Appl. Phys. B 27, 19-25 (1982). 8. K. KAWAGUCHIAND T. TANAKA,J. Mol. Spectrosc. 68, 125-133 (1977). 9. D. DANGOISSE, A. DELDALLE,AND P. GLORIEUX,J. Chem. Phys. 69, 5201-5202 (1978). IO. D. DANG~ISSEAND P. GLORIEUX,Opt. Commun. 32, 246-250 (1980). il. E. AFUMONDO, M. INGUSCIO, A. Mown, M. PELLEGRINO, AND F. STRUMIA,Opt. Lett. 5,496498 (1980). 12. G. BUSSE,E. BASEL,AND A. PFALLER, Appl. Phys. 12, 387-389 (1977). 13. G. DUXBURYAND H. HERMAN,J. Mol. Spectrosc. 73,444-461 (1978). 14. W. J. LAFFERTY,J. P. SADLER, T. L. WORCHESKY,AND K. J. RITTER,.I. Mol. Spectrosc. 87, 416428 (1981). 15. E. J. DANIELEWICZ AND C. 0. WEISS,IEEE J. Quantum Electron. QE14, 705-707 (1978). 16. E. J. DANIELEW(CZ, T. A. GALANTOWICZ,F. B. FOOTE,R. D. REEL,AND D. T. HODGES,Opt. Lett. 4,280-282 (1979). 17. D. R. LIDE,JR., J. Amer. Chem. Sot. 74, 3548-3552 (1952). 18. E. HIROTA,J. Mol. Spectrosc. 69, 409-420 (1978). 19. Y. Y. KWANANDD. M. DENNISON,J. Mol. Spectrosc. 43, 291-319 (1972).
SPECI-ROSCOPY
100,396-402(1983)
Infrared-Microwave Double Resonance as an Aid in Assignment of Optically Pumped Submillimetre Laser Lines: CH&F2, CH2F2, and CH30H J. C. PETERSEN,’
D. IGNER,’
AND G. DUXBURY
Department of Natural Philosophy, University of Strathciyde. 107 Rottenrow, Glasgow G4 ONG. Scotland
Infrared-microwave double resonance has been used to confirm recent assignments of optically pumped submillimeter wave laser lines in CH&F, and CHsOH, as well as a tentative assignment of a line in CF2Hz. Intracavity double resonance signals have also been obtained in CF2CH2 using a circular copper waveguide laser. INTRODUCTION
The assignment of optically pumped laser lines and their parent pump lines is of considerable importance in the modeling of laser behavior. One particular technique which is suitable for this purpose is infrared-microwave double resonance. This is now a well-established technique for spectroscopic studies, both of the ground state and of vibrationally excited states, of molecules absorbing in the infrared. Recently the technique has been used to confirm assignments of submillimeter laser lines in CH30H (I, 2) and to support the existence of an x state close to the C-O stretching state in CH30H (3) postulated by Henningsen (4). Assignments made in this way are particularly important in molecules such as CH30H and CF*Hz, where the excited states are not particularly well characterized. We have recently observed many new optically pumped submillimeterwave laser lines in CHzCFz (5), CHzFz (6), and CH30H (7) using isotopically labeled CO2 lasers. Many of these lines were assigned using primarily wavelength data, and we can now confirm some of these assignments owing to the observation of IRMWDR signals on connected transitions. IRMWDR has not previously been reported to CHzCFz, although signals were observed in CHIFz in the presence of a Stark field (8). Intracavity double resonance experiments to study the active medium of a submillimeter laser were first carried out by a Dangoisse et al. (9, IO) using an open resonator. Arimondo et al. (II) used a similar method to confirm an assignment in CH30H by introducing rf power into a dielectric waveguide. The use of a circular copper waveguide laser in the present experiments increases the microwave power density, and hence a larger effect is expected. Double resonance signals were observed on several submillimeter transitions using three different microwave pumping transitions. ’ present address: Hemberg Institute of Astrophysics, National Research Council Canada, Ottawa, Canada. ’ Formerly of Dept. of Theoretical Chemistry, Bristol University. 0022-2852183 $3.00 Copyright 0 1983 by Academic Press. Inc. All rights of reprcduction in any form resewed.
396
LASER
LINES
OF CH2CF2,
EXPERIMENTAL
CH2F2,
and
CHIOH
397
APPARATUS
In the experiment an extracavity K-band absorption cell was used. The cell was 1.4 m long and terminated at each end by KC1 Brewster windows. The CO2 beam was focused into the cell using two ZnSe lenses and after a double pass the infrared beam was monitored using a PbSnTe detector. The double resonance effect was detected as a change in infrared absorption when the microwave frequency was tuned. The microwave region from 21 to 32 GHz was covered using three high power klystrons (OIU 24V11, 20’12, 3OV12). The microwave power was introduced into the cell via a K-band waveguide mounted perpendicular to the absorption cell. The microwave frequency was modulated at 5 kHz and a voltage ramp was used for scanning the microwave frequency over 150 MHz. The resulting absorption signals were observed using phase-sensitive detection. Parallel polarization of the microwave and infrared fields was used. The frequencies were measured by monitoring beats between the klystron frequency and a Micro-Now frequency multiplication chain, using a radio receiver. The accuracy of the measurements is estimated to *OS MHz. To obtain double-resonance signals within a submillimeter laser cavity a circular copper waveguide laser was used, and the microwaves introduced via a K-band waveguide mounted perpendicular to the tube near one of the mirrors. The submillimeter laser was held tuned to the power peak of the transition being studied while the microwave frequency was slowly swept. The change in the output power of the laser was monitored with a Golay cell detector. OBSERVED
DOUBLE
RESONANCE
SIGNALS
The search for double resonance signals in the three asymmetric top molecules CH2CF2, CHzFz, and CH30H was mainly concentrated on CO2 laser lines where opto-acoustic signals had been observed (22) and corresponding optically pumped submillimeter laser lines had been found.
The CHzCFz molecule has been extensively studied using laser Stark (13) and diode laser spectroscopy (14). In Ref. (24) molecular constants for the u4 (CF2 symm stretch) and u9 (CHz in-plane rocking) vibrational bands have been determined with great accuracy and it has therefore been possible to assign most submillimeter laser lines from the CH2CF2 molecule. The double resonance signals observed in CFzCHz therefore, beside confirming existing assignments, also enable a comparison of the frequency of observed excited state microwave transitions with those calculated using the constants deduced previously (13, 14). Three double resonance signals were observed using CO;? laser lines which are known to act as pump lines for submillimeter laser action. The frequencies and assignments are given in Table I. Two strong double resonance signals were observed when using the ‘3C’602 1OR(14) laser line, which were known to act as a pump for submillimeter emission lines (5). The microwave transitions were assigned using the rotational constants determined by Lafferty et al. (14). The microwave, submillimeter, and infrared transitions are shown in Fig. 1. The infrared absorption transition is a parallel transition in the Q branch of the v4 band. The microwave transitions are K-doublet transitions in the
398
PETERSEN, INGER, AND DLJXBURY TABLE I Assigned Infrared-Microwave Double Resonances in CH2CF2 Observed frequency (MHZ)
Microwave transition
o-c (MHz)
Infrared
transition
"* state (27 22 5) - (27 22 6)
0.0
23363.4
(27 22 6) - (27 22 5) 9.s. (27 22 5) -
vg
(27 22 6)
2
21688=
state
(20 16 4) - (20 16 5)
a - Klystron
operatinq
-0.3
25652.9
at
its
low
frequency
limit and the
(20 16 4) - (20 17 3)
beats
were
unstable.
ground and u4 states. Both share a common level with the infrared transition. A very strong double resonance was observed using the i2Ci602 lOP( 10) laser line. The transition can be assigned to a v9 state K-doublet transition (20 16 4)-(20 16 5), and confirms the assignment of the submillimeter laser line observed using this CO2 pump line. The transitions are shown in Fig. 2. The three microwave transitions were also found to have influence on the output power of the submillimeter waveguide laser when introduced into the cavity. A typical signal is shown in Fig. 3. The ~-MHZ linewidth (FWHM) of the signal is produced mainly by pressure broadening. The signal shown corresponds to the microwave transition shown in Fig. 2. The resonance appears as a sharp decrease in the submillimeter laser power. This can be explained by a change in population. The population in the u9 state is very low at room temperature and the main population here is transferred into level 20L6,4by the CO2 pump laser. The population of this level is depleted by the microwave transition, thus reducing the population inversion responsible for the submillimeter laser oscillation. The 23 363.4-MHz microwave transition in the scheme shown in Fig. 1 caused a decrease in the laser power output while the 2 1 688-MHz microwave transition caused an increase in power. In the latter case the infrared pumping removes a noticeable number of molecules from level 2722,5in the ground state. The high power microwave radiation will try to equalize the populations of the levels 27 22,5and 2722,6in the ground state and more molecules are available for pumping by the laser, leading to an increase in the submillimeter laser power.
The methylene fluoride molecule has been shown to be one of the most efficient submillimeter wave laser molecules in the short wavelength region below 300 pm (15, 16). Tentative assignments of laser lines from this molecule have only recently been made (6). Although the main infrared absorption of the CO2 laser power is expected to be associated with transitions in the v9 (CF2 asym stretch) and the v3 (CF symm stretch)
LASER
LINES
OF CH2CF2, CH2F2, and CH,OH
399
27 22 5
23363.4MHz
27 22 6
26 26
22 4 22 5
FIG. I. Energy level diagram showing the microwave, CH2CF2 using the ‘3C’602 lOR( 14) laser line.
submillimeter
laser, and infrared transitions
in
bands, at 1090.1 and 1113.2 cm-‘, respectively, some absorption may be due to hot band transitions, since the frequency of the v4 band is very low at 528.5 cm-‘. These possibilities, together with strong Coriolis coupling between the u9 and v3 vibrational states, complicate the process of assignment. A very strong double resonance was observed when using the 9R(34) ‘%?OZ laser line. We have previously observed a submillimeter laser line using this pump line and given a tentative assignment for the submillimeter and infrared transitions involved (6). The microwave transition at 23 864.8 MHz had previously been observed and assigned by Lide (17). Its assignment, to the ground state transition (32 8 24) - (3 1 9 23), confkns the previous assignments. All transitions involved are shown in Fig. 4. The microwave transition was calculated using the molecular constants given by Hirota (18). The difference between the cal20 20
19
164 16 5
256529
MHz
164
FIG. 2. Schematic diagram of the energy levels of the VPband of CH,CFz involved in the double resonance experiment.
400
PETERSEN,
INGER,
AND
DUXBURY
MHz
25653
FIG. 3. Change of SMMW laser output power with microwave pump frequency. The laser was tuned to the top of its mode profile. The microwave transition is the 20,6A - 2016,5 transition in the vs state of CHrCFr. The SMMW emission transition is 20,6,4 - 19r6,r. The pressure was ca. 100 mTorr.
culated and measured value for the transition is 2.0 MHz. This is partly due to the fact that the rotational constants were derived from transitions with J d 20 and K, =S6 (18). The transition (33 8 25)-(33 7 26) in the u9 state is a potential laser transition, with a calculated wavelength of 535.4 pm. CH30H This molecule is one of the most studied submillimeter laser gases, and accounts for more than 200 laser lines (4), but its spectrum is still not completely understood. This is partly due to the complexity of the hindered internal rotation of the hydroxyl group with respect to the methyl group and its interaction with other vibrational modes. Any additional information on the spectrum is therefore very important. A double resonance signal was observed when using the ‘2C’802 9P( 16) pump line. This line has previously been used for generation of three very strong submillimeter laser lines, all of which could be assigned (7). These lines together with the microwave transition are shown in Fig. 5. The microwave transition was measured to be 30 189.8 MHz, and could be assigned to the (017, 27)-(038, 26) ground state transition, using calculations based on the molecular constants and Hamiltonian of Kwan and Dennison (I 9). 33 825 33 826
T
“C ‘q
LASER
9Rl341
Rc. 4. Energy level scheme for the (33 8 25) - (32 8 24) transition of CHrFr of the v9 band probed by the 9R(34) ‘2C’802 laser line. The submillimeter wave laser transition is shown in the excited state, and the microwave pump transition in the ground state. K-doublet splittings are not to scale.
LASER LINES OF CH2CF2, CHzFz, and CHsOH
401
28 27
44.61 cti’
“C”Q
i
026
017
LASER 9Pil6)
038
flTK
FIG. 5. Energylevel scheme for the QR(O17,27) transitionof CH3OH pumped by the 9P(16) ‘*C’*O2 laserline. FIR transitionsare shown in the excited state and the microwave probe transition is shown in the ground state.
CONCLUSION
We have observed several double resonance signals in CH2CF2, CH2F2, and CH30H which have all confirmed our original assignments of optically pumped submillimeter laser lines. Several other double resonance signals which could not be associated with submillimeter laser action were observed in the region 2 l-32 GHz. These comprise four double-resonance signals in CH2CF2 and four signals in CHzFz . Analysis of these is in progress. RECEIVED: April
5,
1983 REFERENCES
I. 2. 3. 4.
R. M. LEES,C. YOUNG, J. VAN DERLINDE,AND B. A. OLIVER,J. Mol. Spectrosc.75, 161-167 (1979). C. YOUNG, R. M. LEES,J. VAN DERLINDE,AND B. A. OLIVER,J. Appl. Phys. 50, 3808-38 10 (1979). R. M. LEES,M. A. WALTON,AND J. 0. HENNINGSEN, J. Mol. Spectrosc. 88, 90-94 (I 98 I). J. 0. HENNINGSEN, J. Mol. Spectrosc. 83, 70-93 (1980).
402
PETERSEN,
INGER,
AND DUXBURY
5. J. M~COMBIE,J. C. PETERSEN, AND G. DUXBURY, in “Quantum Electronicsand Electra-Optics,” (P. L. Knight, Ed.), pp. 251-253, Wiley, New York, 1983. 6. J. C. PETERSEN AND G. DUXBURY,ht. J. IR and Mm Waves 3, 607-618 (1982). 7. J. C. PETERSEN ANLIG. DUXBURY,Appl. Phys. B 27, 19-25 (1982). 8. K. KAWAGUCHIAND T. TANAKA,J. Mol. Spectrosc. 68, 125-133 (1977). 9. D. DANGOISSE, A. DELDALLE,AND P. GLORIEUX,J. Chem. Phys. 69, 5201-5202 (1978). IO. D. DANG~ISSEAND P. GLORIEUX,Opt. Commun. 32, 246-250 (1980). il. E. AFUMONDO, M. INGUSCIO, A. Mown, M. PELLEGRINO, AND F. STRUMIA,Opt. Lett. 5,496498 (1980). 12. G. BUSSE,E. BASEL,AND A. PFALLER, Appl. Phys. 12, 387-389 (1977). 13. G. DUXBURYAND H. HERMAN,J. Mol. Spectrosc. 73,444-461 (1978). 14. W. J. LAFFERTY,J. P. SADLER, T. L. WORCHESKY,AND K. J. RITTER,.I. Mol. Spectrosc. 87, 416428 (1981). 15. E. J. DANIELEWICZ AND C. 0. WEISS,IEEE J. Quantum Electron. QE14, 705-707 (1978). 16. E. J. DANIELEW(CZ, T. A. GALANTOWICZ,F. B. FOOTE,R. D. REEL,AND D. T. HODGES,Opt. Lett. 4,280-282 (1979). 17. D. R. LIDE,JR., J. Amer. Chem. Sot. 74, 3548-3552 (1952). 18. E. HIROTA,J. Mol. Spectrosc. 69, 409-420 (1978). 19. Y. Y. KWANANDD. M. DENNISON,J. Mol. Spectrosc. 43, 291-319 (1972).