Harold Jones

Infrared-microwave two-photon spectroscopy with13C16O2 and12C18O2 lasers of the ν2-band of ammonia

A tunable microwave frequency was added to, or subtracted from fixed frequency13C16O2 and12C18O2 laser lines using the nonlinearity of molecular absorptions. In this way the frequency of 30 transitions of the ν2-band of ammonia were measured with an accuracy of ±0.0005 cm−1. A further four transitions were measured with an accuracy of ±0.0001 cm−1 by saturating the two-photon transition and observing the Lamb dip. For laser lines up to 11 GHz off-resonant with in frared transitions Doppler-limited signals were observed with microwave power densities of only 10 mW/cm2 using a wide-band intracavity cell.

Two-photon spectroscopy of 15NH3 with isotopic CO2 lasers and double resonance studies with a new coincidence

Abstract Eleven transitions of the ν2 band of 15NH3 were measured by the technique of infrared-microwave two-photon spectroscopy using an isotopic CO2 laser and 20-mW microwave power. By combining these results with those of previous two-photon measurements and with Stark laser spectroscopy results, the spectroscopic constants of this band were calculated. Using the previously unknown coincidence between the R(18) 13CO2 laser line and the asQ(5,4) infrared transition, velocity tuned multiple-photon Lamb-dip signals were observed. Very intense double resonance signals were observed on the (5,4), (6,4), and (4,4) microwave transitions and the magnitude of these effects was compared to those observed previously in 14NH3.

Infrared-microwave double resonance in CF3I; Microwave spectroscopy in emission and absorption☆

Abstract From the double resonance effects observed on the microwave spectrum of CF3I it has been shown that the R(16) CO2 laser line of the 9.4 μm band is coincident with the R(7), K = 2, F = 19 2 → 21 2 transition of the CF3, symmetric stretch (ν1 band) of CF3I. Using this laser line, 50 double resonance signals all with K = 2 were observed ranging from J = 4 → 5 to J = 12 → 13 transition. The fact that double resonance effects were observable over such a large range of J was explained as being caused by very strong ΔJ = ± 1, ΔK = 0 collisional transitions. Extremely large pumping effects were produced using 6 W of laser radiation, which caused relative changes in intensity ( Δ I I ) in ground state lines of up to 25. The population transfer into the excited state was so large that many excited state lines, which had previously been undetectable, produced signals up to 30 times more intense than the corresponding undisturbed ground state lines (i.e., values of Δ I I of ∼6000 were achieved). Population inversions were produced by the laser pump in many of the K = 2 microwave transitions, not only in those with levels directly pumped by the laser but also in some connected only by collisional transitions. The results was that many of the signals were observed as stimulated emissions rather than absorptions. The rotational constant and quadrupole coupling constants of CF3I in the v1 excited state are calculated and an estimation of the center of the ν1 band is made. The absolute population shifts produced by the laser pump are estimated and the rate constants of the collisional transitions are discussed.

The ground state infrared spectra of several isotopic forms of the CdH and ZnH radicals

The infrared spectra of six isotopic forms of cadmium monohydride, [116CdH (7.6%), 114CdH (28.9%), 113CdH (12.3%), 112CdH (24.1%), 111CdH (12.7%), and 110CdH (12.4%)] and four isotopic forms of zinc hydride [68ZnH (18.6%), 67ZnH (4.1%), 66ZnH (27.8%), and 64ZnH (48.9%)] have been observed in natural abundance in their ground electronic state (2∑+) in the gas phase using a diode laser spectrometer. A number of transitions of 108CdH (0.9%) and 106CdH (1.2%) and 70ZnH (0.6%) were also observed, but too little data was accumulated to allow a good analysis. The hydrides were produced by reaction of hydrogen with metal vapor at elevated temperature in an electric discharge. The analysis of the experimental data was carried out in two ways. (a) A complete set of Dunham parameters and spin–rotation parameters (γ parameters) was determined for each isotopic species of the two radicals and (b) a set of mass‐independent parameters were calculated for both ZnH and CdH. Since only information over the isotopic species...

Laser-microwave two-photon and double resonance spectroscopy of two linear molecules; HCCF and FCN

Abstract The technique of laser-microwave two-photon spectroscopy has been used to determine the frequencies of a number of transitions in fundamental and hot-bands of the two linear molecules HCCF and FCN. This method has previously only been applied in a systematic way to spectroscopy in NH 3 and it was the aim of this investigation to determine to what extent this method was applicable to more normal molecular species. The maximum effective tuning range produced with these molecules was ±3.7 GHz with a microwave power density of ⋍100 mW/cm 2 and a laser power density of ⋍40 W/cm 2 . Transition frequencies were determined with accuracies up to ±3 MHz using a Lamb-dip technique. In the case of fluoroacetylene the observation of a number of double resonance signals involving direct l -type doubling transitions allowed determination of l -type doubling constants for the states ( v 3 = 1, v 4 = 1) and ( v 3 = 1, v 5 = 1). The P (12) C 18 O 2 laser line was shown to lie within the Doppler width of the upper l -type doublet R (25) transition of the ( ν 3 + ν 4 ) − ν 3 hot band. In this particular case velocity-tuned multiple photon dips were observed. The dispersive component of double resonance and two-photon Lamb-dip signals was observed to have opposite phase in two different vibrational states. The possible diagnostic value of this observation is discussed.

Precision infrared spectroscopy in CF379Br by means of infrared-microwave double resonance

Abstract From the observation of double resonance effects on the microwave spectrum two coincidences between 9.4 μm CO 2 laser lines and infrared transitions of the ν 6 → (ν 6 + ν 1 ) band of CF 3 79 Br have been determined: R (30) laser line coincident with q R 2 (7), F = 17/2→17/2 transition, R (28) laser line coincident with all four Δ F = 0 hyperfine components of the q Q 8 (13) transition. In both cases other infrared transitions lay within the tuning range of the laser. The frequencies of these two laser lines allowed calculations of the band center frequency ν 0 = 1083.530 ± 0.001cm −1 and α A = 11.93 ± 0.3MHz, for the ν 6 → (ν 6 + ν 1 ) band.α B constants were determined for the vibrational states v 6 , ( v 6 + v 1 ), v 1 , and v 3 .

The 923-cm−1 band of CF235Cl2 (freon 12), studied by infrared-microwave double resonance

Abstract The constants of the 923-cm −1 band ( ν 6 ) of CF 2 35 Cl 2 were accurately determined by the application of infrared-microwave double resonance using CO 2 and N 2 O lasers. The frequencies of 32 ground-state and 34 ( v 6 = 1) state rotational transitions and 14 infrared transitions were measured. The infrared transition frequencies were generally obtained with an accuracy of ± 20 MHz, but in some cases observation of two-photon Lamb-dips allowed the accuracy to be improved to ± 5 MHz. Many double-resonance signals displayed a predominantly “dispersion-type” lineshape and it has been shown that the phase of the observed signals gives information over the relative disposition of the energy levels involved.

Infrared-microwave double-resonance spectroscopy of the ClO2 radical: A textbook example

Abstract The capability of the ir-mw double-resonance technique to produce precise spectroscopic data has been thoroughly tested in a study of the ClO2 free radical. Although the experiments are based on fixed-frequency gas lasers, the results of the work show that rotational and vibrational information can be obtained from practically all infrared absorption bands of ClO2 within the operating frequency range of the lasers. A wide range of microwave frequencies was searched using approximately 120 individual laser lines; double-resonance signals were observed with about 25% of the lines used. The double-resonance data obtained were sufficient to determine rotational, distortion, fine, and hyperfine constants for the vibrational states (0, 0, 0), (1, 1, 0), and (0, 0, 1) of 35ClO2 and (1, 0, 0) and (0, 0, 1) for 37ClO2. The constants for the (0, 0, 0) state of 35ClO2 and 37ClO2 and for (0, 1, 0) of 35ClO2 were refined and those for the (0, 1, 0) state of 37ClO2 were determined with data obtained from double-resonance and conventional measurements. The rotational constants obtained allowed equilibrium structures for both 35ClO2 and 37ClO2 to be calculated. The structural parameters obtained in each case are in excellent agreement: r e = 1.4700(1 A ) , θe = 117° 23.3′(7). The centers of the bands ν1 and ν1 + ν2 − ν2 of 35ClO2 were precisely determined and the data available were sufficient to check the reliability of the values obtained. The band origins were also determined for ν3, 35ClO2 and 37ClO2, and with less precision for ν1 for 37ClO2.

Laser-microwave double-resonance spectroscopy in CF3I with four CO2-laser lines

Abstract Double-resonance effects produced by three CO 2 -laser lines, the 9.4- μ m R (12), R (14), and R (18), have been newly observed. From an analysis of the observed laser-induced changes in intensity of various microwave transitions, the infrared transitions which were accidentally coincident with these three laser lines were determined. In every case an exact rotational assignment of the infrared transition was possible, but in some cases the assignment of the vibrational band involved was difficult. When the previously discussed ( l ) effects produced by the R (16) laser line are included these four consecutive laser lines pump a total of seven infrared transitions of CF 3 I. It appears that all seven transitions belong to different fundamental, combination, and hot bands.

Wide-band intracavity microwave cells for laser-microwave double resonance spectroscopy

The design and use of two wide-band microwave cells suitable for double resonance experiments within the resonator of a cw CO2-laser are described. The high sensitivity of the intracavity arrangement allowed very strong double-resonance and two-photon transition signals to be observed with high microwave-frequency scan-rates (1 GHz/min), and low microwave pumping powers (≦10mW/cm2). Both cells were used over a range 15 to 63 GHz, with transmission and VSWR measurements made over the range 18 to 26.5 GHz.