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FIR laser assignments in CHD2F
Infrared Phys. Vol. 23, No. 4, pp. 233 734, 1983 Printed in Great Britain
0020-0891 :x3 S3.00+0.00 Pergamon Preaa Ltd
TECHNICAL NOTE FIR
LASER
ASSIGNMENTS
IN CHD,F
D. F. EGGERS Department
of Chemistry,
University (Received
of Washington. 13 Fehruur~
Seattle,
WA
98195.
U.S.A
1983)
Abstract-A sample of CHD,F was synthesized and its ix. spectrum was measured in the 900-1200 cm ’ region at 0.03 cm-’ resolution. A portion of this sample was optically pumped with a “C’h02 laser in another laboratory. A number of FIR laser lines were produced, including several cascade transitions. We discuss assignments of the pumped transitions and of the FIR emission in relationship to the ix. spectrum. We show that one of these new FIR lines is the same as a line observed earlier in optical pumping of CD,F; it was thus due to a small amount of CHDzF present in the CD,F sample. We suggest further that several OODR signals reported in CD,F, but not assigned, were also due to some CHD,F impurity.
Although a large number of molecules have been found to produce coherent FIR emission when they are pumped with CO, lasers in a suitable cavity, the majority of such laser lines are too weak for a number of applications. It is important, therefore, to find additional molecules that produce FIR with good efficiency, and thus to fill in the gaps between known strong lines from a small number of molecules that give useful output powers. Four different isotopic forms of methyl fluoride have been shown to produce FIR laser output. when optically pumped with CO? lasers: “CH,F,“) “CH,F,“’ “CD,F”’ and ‘3CD,F.(4’ Some of these transitions can produce substantial output powers. The partially-deuterated molecule “CHD?F shares many of the properties of the other methyl fluorides that help make them useful as optically-pumped sources; that is, a large dipole moment, small moments of inertia and intense vibrations absorbing in the region of CO, laser output. It also appeared that CHDzF had never been tested for FIR laser emission. We have, therefore, synthesized a sample of CHD,F, in isotopic purity above 9Y,,. examined its i.r. spectrum in the 900-1200cmregion, and sent a sample to Dr M. S. Tobin for testing in an optically-pumped CO, laser apparatus. Nine different ‘2C’602 laser lines were found to produce FIR output; frequencies were measured for a number of them, by heterodyne techniques.“’ Three of these nine coincidences of molecular absorption with CO? laser emission can be assigned confidently from our preliminary analysis of the spectrum. Suggestions are presented for three others, though further work may show some need for revisions. The- three coincidences readily assigned are all found in the vh band that has an origin about 965.5 cm-‘. These three firm assignments are presented first, followed by tentative suggestions for three additional observed coincidences. The 1OR26 line pumps JKt,,Kh= 1O,,,+-9,, and 10,,+9,,, ; the 9,,,~+8,,, and 96,~~+8,,2. The FIR is from 106,5+9(,,, and I 06,4-t96,3, p lus the cascade transitions 1OR20 line pumps 8,,e+-72,, or 82,,t72,, ; the FIR is from 82,6+ 72,s or 8?,,’ 72,6. The 1OP28 line pumps 18,,,, ~19~,,? and 18,.,Zc19,,,,; the FIR is 187,,,~177,,0 and 18,,,Z-,17 ,,,,, plus thecascade transitions The asymmetry splitting for Ka = 2 should be much larger than the 17,,,,,+ 16,,, and I7,., I- 16~~~o~ CO? laser linewidth, but the separation is apparently not resolved in our spectrum at 0.03 cm-’ resolution. The asymmetry splitting for levels with Ku of 6 and 7 is expected to be much less than the CO, laser linewidth. All three of these i.r. absorptions are sharp and apparently not overlapped by other transitions. The lOR38 line also produces FIR output; however, the i.r. spectrum shows a blended line at this position, with J and Ku values still uncertain. We suspect it can probably be assigned to the vg state as well, but perhaps with perturbation from another state. Two other FIR laser emissions whose frequencies have been measured must originate in other vibrational states. The 10P46 line produces output at such a long wavelength that it must be associated with a J value less than 10. This, together with the location of the 10P46 line, at 918.718 cm-‘, means that the very weak vq perpendicular band is responsible. The 9R6 pumping 233
line. at 1069.014 cm ‘. is less than 20 cm ’ from the origin of the I’, hand. about 1050cm furthermore. the approximate J value deduced from the FIR wavelength is ton fall for aaignmcnt of the pumped level to I’~. centered at about 1094 cm ‘. The observation of several cascade transitions. noted above. was moht intcrcstlng. T.h14\uggc\t\ that the FIR generation may have quite good efficiency. The strength of the IOP?S pumping I\ also indicated by the fact that this same emission seems to be found. though weahl~. from ;I ~mplc of CD,F.“’ Dividing the FIR frequency produced upon pumping the (‘D;l- ~mplc with IOPZS b\ twice the 8 value in the II,>state of CD,F”” leads to 19.22. as an estimate 01‘ the f:IR cmlttlng \tatc J value. This is too far from an integer. lending further support to the claim that the I;111 Iahing in the C’D:F is actually due to ;I ftw per cent of CHD,F present in the C‘II,t-’ wmplc Such ;I concentration is expected, from the stated isotopic purities in most all commcrc~;~I ~mplc\ It is interesting to note that both C’D,F and CHD,F produce f-IR output from the 9,Pl(l and from the IOP46 CO, lines. However. the emission wavelengths are sub~tantiall\ dill-crcnt bct\\ccn the two isotopes, showing that the FIR generated when the CD,F sample i\ p~~~~~ptxi \\ith e~thcr 9P16 or 10P46 must originate in the CD;F molecule, and not in the CHD,F imperil>. FIR emission from the isotopic impurity in a C‘D:F sample led uh to look for Gmilar cltccrs III other work. Some recent observations of Duxbury and Kato’T” on optical optical double raonancc in CD,F can be understood on the basis of a small amount ofCHD:F in their s:tmplc. Specilically. they reported strong OODR signals at 1050.494 and 1091.3X9 cm ’ uhen using ;I “(“‘0 I;IUY: the conditions of observation required that these signals involve either .I = 2. h’ = I or .I = 3. h -=-2. Since the OODR signals are at least 23 cm ’ from the nearest band origins ot‘ C‘I>:i-. quantum numbers so small are not possible. However. since the band centers in (‘H D>F arc abon~ 1050 cm for V, and 1094 cm ’ for V, these could well explain the OODR signal\. We recently made arrangements with Dr Duxbury. and sent a sample of CHD2F for study in the OODR apparatu\: he reports from preliminary work that there are indeed a number of OODR signals I‘rom thl\ sample, and that they are generally stronger than the lines observed in <‘D,t’.“’ Our sample was prepared in five steps, with deuterated acetone ;I\ the starting material. Hoaacr. CHD,F should be formed in one step from C’HCI,F. with use of-a suitable acti\c metal dcuteridc. The CHCI,F is commercially available al low cost. rcg~on M ill bc published Results of the detailed analysis of the four bands in the c)OO-I100 cm elsewhere.
0020-0891 :x3 S3.00+0.00 Pergamon Preaa Ltd
TECHNICAL NOTE FIR
LASER
ASSIGNMENTS
IN CHD,F
D. F. EGGERS Department
of Chemistry,
University (Received
of Washington. 13 Fehruur~
Seattle,
WA
98195.
U.S.A
1983)
Abstract-A sample of CHD,F was synthesized and its ix. spectrum was measured in the 900-1200 cm ’ region at 0.03 cm-’ resolution. A portion of this sample was optically pumped with a “C’h02 laser in another laboratory. A number of FIR laser lines were produced, including several cascade transitions. We discuss assignments of the pumped transitions and of the FIR emission in relationship to the ix. spectrum. We show that one of these new FIR lines is the same as a line observed earlier in optical pumping of CD,F; it was thus due to a small amount of CHDzF present in the CD,F sample. We suggest further that several OODR signals reported in CD,F, but not assigned, were also due to some CHD,F impurity.
Although a large number of molecules have been found to produce coherent FIR emission when they are pumped with CO, lasers in a suitable cavity, the majority of such laser lines are too weak for a number of applications. It is important, therefore, to find additional molecules that produce FIR with good efficiency, and thus to fill in the gaps between known strong lines from a small number of molecules that give useful output powers. Four different isotopic forms of methyl fluoride have been shown to produce FIR laser output. when optically pumped with CO? lasers: “CH,F,“) “CH,F,“’ “CD,F”’ and ‘3CD,F.(4’ Some of these transitions can produce substantial output powers. The partially-deuterated molecule “CHD?F shares many of the properties of the other methyl fluorides that help make them useful as optically-pumped sources; that is, a large dipole moment, small moments of inertia and intense vibrations absorbing in the region of CO, laser output. It also appeared that CHDzF had never been tested for FIR laser emission. We have, therefore, synthesized a sample of CHD,F, in isotopic purity above 9Y,,. examined its i.r. spectrum in the 900-1200cmregion, and sent a sample to Dr M. S. Tobin for testing in an optically-pumped CO, laser apparatus. Nine different ‘2C’602 laser lines were found to produce FIR output; frequencies were measured for a number of them, by heterodyne techniques.“’ Three of these nine coincidences of molecular absorption with CO? laser emission can be assigned confidently from our preliminary analysis of the spectrum. Suggestions are presented for three others, though further work may show some need for revisions. The- three coincidences readily assigned are all found in the vh band that has an origin about 965.5 cm-‘. These three firm assignments are presented first, followed by tentative suggestions for three additional observed coincidences. The 1OR26 line pumps JKt,,Kh= 1O,,,+-9,, and 10,,+9,,, ; the 9,,,~+8,,, and 96,~~+8,,2. The FIR is from 106,5+9(,,, and I 06,4-t96,3, p lus the cascade transitions 1OR20 line pumps 8,,e+-72,, or 82,,t72,, ; the FIR is from 82,6+ 72,s or 8?,,’ 72,6. The 1OP28 line pumps 18,,,, ~19~,,? and 18,.,Zc19,,,,; the FIR is 187,,,~177,,0 and 18,,,Z-,17 ,,,,, plus thecascade transitions The asymmetry splitting for Ka = 2 should be much larger than the 17,,,,,+ 16,,, and I7,., I- 16~~~o~ CO? laser linewidth, but the separation is apparently not resolved in our spectrum at 0.03 cm-’ resolution. The asymmetry splitting for levels with Ku of 6 and 7 is expected to be much less than the CO, laser linewidth. All three of these i.r. absorptions are sharp and apparently not overlapped by other transitions. The lOR38 line also produces FIR output; however, the i.r. spectrum shows a blended line at this position, with J and Ku values still uncertain. We suspect it can probably be assigned to the vg state as well, but perhaps with perturbation from another state. Two other FIR laser emissions whose frequencies have been measured must originate in other vibrational states. The 10P46 line produces output at such a long wavelength that it must be associated with a J value less than 10. This, together with the location of the 10P46 line, at 918.718 cm-‘, means that the very weak vq perpendicular band is responsible. The 9R6 pumping 233
line. at 1069.014 cm ‘. is less than 20 cm ’ from the origin of the I’, hand. about 1050cm furthermore. the approximate J value deduced from the FIR wavelength is ton fall for aaignmcnt of the pumped level to I’~. centered at about 1094 cm ‘. The observation of several cascade transitions. noted above. was moht intcrcstlng. T.h14\uggc\t\ that the FIR generation may have quite good efficiency. The strength of the IOP?S pumping I\ also indicated by the fact that this same emission seems to be found. though weahl~. from ;I ~mplc of CD,F.“’ Dividing the FIR frequency produced upon pumping the (‘D;l- ~mplc with IOPZS b\ twice the 8 value in the II,>state of CD,F”” leads to 19.22. as an estimate 01‘ the f:IR cmlttlng \tatc J value. This is too far from an integer. lending further support to the claim that the I;111 Iahing in the C’D:F is actually due to ;I ftw per cent of CHD,F present in the C‘II,t-’ wmplc Such ;I concentration is expected, from the stated isotopic purities in most all commcrc~;~I ~mplc\ It is interesting to note that both C’D,F and CHD,F produce f-IR output from the 9,Pl(l and from the IOP46 CO, lines. However. the emission wavelengths are sub~tantiall\ dill-crcnt bct\\ccn the two isotopes, showing that the FIR generated when the CD,F sample i\ p~~~~~ptxi \\ith e~thcr 9P16 or 10P46 must originate in the CD;F molecule, and not in the CHD,F imperil>. FIR emission from the isotopic impurity in a C‘D:F sample led uh to look for Gmilar cltccrs III other work. Some recent observations of Duxbury and Kato’T” on optical optical double raonancc in CD,F can be understood on the basis of a small amount ofCHD:F in their s:tmplc. Specilically. they reported strong OODR signals at 1050.494 and 1091.3X9 cm ’ uhen using ;I “(“‘0 I;IUY: the conditions of observation required that these signals involve either .I = 2. h’ = I or .I = 3. h -=-2. Since the OODR signals are at least 23 cm ’ from the nearest band origins ot‘ C‘I>:i-. quantum numbers so small are not possible. However. since the band centers in (‘H D>F arc abon~ 1050 cm for V, and 1094 cm ’ for V, these could well explain the OODR signal\. We recently made arrangements with Dr Duxbury. and sent a sample of CHD2F for study in the OODR apparatu\: he reports from preliminary work that there are indeed a number of OODR signals I‘rom thl\ sample, and that they are generally stronger than the lines observed in <‘D,t’.“’ Our sample was prepared in five steps, with deuterated acetone ;I\ the starting material. Hoaacr. CHD,F should be formed in one step from C’HCI,F. with use of-a suitable acti\c metal dcuteridc. The CHCI,F is commercially available al low cost. rcg~on M ill bc published Results of the detailed analysis of the four bands in the c)OO-I100 cm elsewhere.