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Doppler-free transition frequencies for v4- and v5-excited hot bands have been measured in the v1 + v3 band region of the spectrum of acetylene using saturation dip spectroscopy with an extended cavity diode laser referenced to a frequency comb. The frequency accuracy of the measured transitions, as judged from line shape model fits and comparison to known frequencies in the v1 + v3 band itself, is between 3 and 22 kHz. This is some three orders of magnitude improvement on the accuracy and precision of previous line position estimates that were derived from the analysis of high-resolution Fourier transform infrared absorption spectra. Comparison to transition frequencies computed from constants derived from published Fourier transform infrared spectra shows that some upper rotational energy levels suffer specific perturbations causing energy level shifts of up to several hundred MHz. These perturbations are due to energy levels of the same rotational quantum number derived from nearby vibrational levels that become degenerate at specific energies. Future identification of the perturbing levels will provide accurate relative energies of excited vibrational levels of acetylene in the 7100–7600 cm−1 energy region.

Hyperfine-resolved saturation spectra were measured for a selection of low and medium J rotational lines in the A 2Π–X 2Σ+ system of CN using two copropagating laser beams tuned to transitions in the (2–0) and (1–0) bands. A bleach laser was amplitude modulated and fixed in frequency near the center of a rotational line of the (2–0) vibrational band, while a probe laser was frequency-modulated and scanned across selected lines of the (1–0) vibrational band, sharing a common lower state with the bleach laser. Locking the probe laser with a tunable radio frequency offset to a cavity that tracks the slowly drifting bleach laser greatly improved the quality of the double-resonance saturation signals, by stabilizing the relative frequency of the two beams. The sub-Doppler resonances were fit with Lorentzian line shapes having a typical full-width at half maximum of 2–3 MHz. The hyperfine spectra observed depend on the hyperfine structure within both rovibronic transitions excited, permitting the determination of hyperfine molecular constants in the υ = 2 state and the refinement of previously published values in the υ = 1 state. Four nuclear magnetic dipole and two electric quadrupole hyperfine constants were determined for each of the upper states from a fit with a weighted root mean squared error of 0.5 MHz. The vibrational dependence of these constants is weak or negligible.

The P(11) line of the ν1 + ν3 combination band of C2H2 was studied using an extended cavity diode laser locked to a frequency comb. Line shapes were measured for acetylene and nitrogen gas mixtures at a series of temperatures between 125 and 296 K and total pressures up to 1 atm. The data were fit to two speed-dependent line shape models and the results were compared. Line shape parameters were determined by simultaneously fitting data for all temperatures and pressures in a single multispectrum analysis. Earlier pure acetylene measurements [Cich et al. Appl. Phys. B 2012, 109, 373-38] were incorporated to account for self-perturbation. The resulting parameters reproduce the observed line shapes for the acetylene-nitrogen system over the range of temperatures and pressures studied with average root-mean-square observed-calculated errors of individual line measurement fits of approximately 0.01% of maximum transmission, close to the experimental signal-to-noise ratios. Errors in the pressure measurements constitute the major systematic errors in these measurements, and a statistical method is developed to quantify their effects on the line shape parameters for the present system.

Hyperfine splittings were measured in selected rotational lines of the (1–0) vibrational band of the B ∼ 3 Π g - A ∼ 3 Σ u + transition of 14 N 2 in a low pressure discharge. Frequency modulated saturation dip spectroscopy produced hyperfine resolved, sub-Doppler lines with typical full-width at half-maximum line widths of 7 MHz. Hyperfine transitions within 27 rotational lines in the R 33 , Q 33 , Q 21 , Q 22 , R 11 , and Q 11 branches were recorded for J between 2 and 12, and fit with the same Hamiltonian used previously by Geisen, Neuschafer and Ottinger [Z. Phys. D 4 , 263 (1987)]. The resulting parameters are (in MHz, with one standard deviation in parentheses): α = 13.19(13), β = −12.36(18), e 2 q 0 Q = −1.19(25) for the ( v ″ = 0 ) A ∼ 3 Σ u + state; and K 11 = 98.52(50), D 11 = 13.09(59), D 1−1 = −44.11(16), G 11 = 70.00(52), Q 11 = 1.390(98) and Q 1−1 = 1.65(11) for the ( v ′ = 1) B ∼ 3 Π g state.

Using an extended cavity diode laser referenced to a femtosecond frequency comb, the P(11) absorption line in the ν 1+ν 3 combination band of the most abundant isotopologue of pure acetylene was studied at temperatures of 296, 240, 200, 175, 165, 160, 155, and 150 K to determine pressure-dependent line shape parameters at these temperatures. The laser emission profile, the instrumental resolution, is a Lorentz function characterized by a half width at half the maximum emission (HWHM) of 8.3×10−6 cm−1 (or 250 kHz) for these measurements. Six collision models were tested in fitting the experimental data: Voigt, speed-dependent Voigt, Rautian–Sobel’man, Galatry, and two Rautian–Galatry hybrid models (with and without speed-dependence). Only the speed-dependent Voigt model was able to fit the data to the experimental noise level at all temperatures and for pressures between 3 and nearly 360 torr. The variations of the speed-dependent Voigt profile line shape parameters with temperature were also characterized, and this model accurately reproduces the observations over their entire range of temperature and pressure.

We report measurements of self- and nitrogen-pressure broadening of the P(11) line in the ν 1 + ν 3 combination band of acetylene at 195 739.649 5135(80) GHz by absorption of radiation emitted by an extended cavity diode laser referenced to a femtosecond frequency comb. Broadening, shift and narrowing parameters were determined at 296 K. For the most appropriate, hard collision, model in units of cm −1 /atm, we find 0.146317(27), 0.047271(104) and −0.0070819(22) for the acetylene self-broadening, narrowing and shift, and 0.081129(35), 0.022940(74) and −0.0088913(25) respectively, for the nitrogen-broadening parameters. The uncertainties are expressed as one standard deviation (in parenthesis) in units of the last digit reported. These parameters are 2–3 orders of magnitude more precise than those reported in previous measurements. Similar analyses of the experimental data using soft collision and simple Voigt lineshape models were made for comparison.

Based on measurements made by mass-resolved 1 + 1{prime} + 1{double_prime} resonance-enhanced multiphoton ionization spectroscopy, we have determined new molecular constants describing the rotational and fine structure levels of the B, D, E, and F states of the most abundant isotopic variant {sup 208}Pb{sup 19}F, and we summarize the spectroscopic constants for all the know electronic states of the radical. Many spectroscopic constants for the isotopologues {sup 206}Pb{sup 19}F and {sup 207}Pb{sup 19}F have also been determined. The symmetry of the D-state is found to be {sup 2}{pi}{sub 1/2}, and the F-state is found to be an {Omega} = 3/2 state.

A highly efficient pseudo continuous resonance enhanced multiphoton ionisation detection scheme is presented that combines the sensitivity of resonance enhanced multiphoton ionisation (REMPI) with high resolution. This detection scheme is employed to obtain the A(v′ = 1) ← X 1(v = 0) spectra of 208Pb19F with a resolution of 90 MHz. The observed 19F hyperfine splittings are analysed in terms of effective hyperfine parameters that describe the interaction between the fluorine nuclear spin and that of the unpaired electron in the A and X 1 states of the molecule.

We introduce a new laser detection scheme for the OH radical that employs 1+1 X 2 Π ⇄ D2Σ - resonance enhanced excitation to a high-lying Rydberg state followed by field ionization. We place an upper limit of 8 ns on the lifetime of the D 2 Σ - state. We also correct published values for To for the D 2 Σ - state, provide a new value for the energy of the 6s 1 1 1p 1 3 P 1 0 state of Hg (81 807.6 cm - 1 ), and measure the rotational temperature of OH radicals produced in the photolysis of formic acid at 212.6 nm to be 300 ′ 50 K. Our REMPI probe might be suited to studies that require both sensitive detection of the OH radical combined with accurate kinetic energy information.

Hyperfine-resolved saturation spectra were measured for a selection of low and medium J rotational lines in the A 2Π–X 2Σ+ system of CN using two copropagating laser beams tuned to transitions in the (2–0) and (1–0) bands. A bleach laser was amplitude modulated and fixed in frequency near the center of a rotational line of the (2–0) vibrational band, while a probe laser was frequency-modulated and scanned across selected lines of the (1–0) vibrational band, sharing a common lower state with the bleach laser. Locking the probe laser with a tunable radio frequency offset to a cavity that tracks the slowly drifting bleach laser greatly improved the quality of the double-resonance saturation signals, by stabilizing the relative frequency of the two beams. The sub-Doppler resonances were fit with Lorentzian line shapes having a typical full-width at half maximum of 2–3 MHz. The hyperfine spectra observed depend on the hyperfine structure within both rovibronic transitions excited, permitting the determination of hyperfine molecular constants in the υ = 2 state and the refinement of previously published values in the υ = 1 state. Four nuclear magnetic dipole and two electric quadrupole hyperfine constants were determined for each of the upper states from a fit with a weighted root mean squared error of 0.5 MHz. The vibrational dependence of these constants is weak or negligible.

A cavity perturbation technique is used to study the microwave response of the organic superconductor $\ensuremath{\kappa}\ensuremath{-}(\mathrm{BEDT}\ensuremath{-}\mathrm{TTF}{)}_{2}\mathrm{Cu}(\mathrm{NCS}{)}_{2}.$ Observation of a Josephson plasma resonance, below ${T}_{c}$ $(\ensuremath{\sim}10 \mathrm{K}),$ enables investigation of the vortex structure within the mixed state of this highly anisotropic, type-II superconductor. Contrary to previous assumptions, frequency-dependent studies (28\char21{}153 GHz) indicate that the squared plasma frequency $({\ensuremath{\omega}}_{p}^{2})$ depends exponentially on the magnetic-field strength. Such behavior has been predicted for a weakly pinned quasi-two-dimensional vortex lattice [Bulaevskii et al., Phys. Rev. Lett. 74, 801 (1995)]. Our data also suggests a transition in the vortex structure near the irreversibility line.

Selected isolated rotational transitions in the 1-0 band of the red A(2)Π-X (2)Σ(+) system in CN have been recorded with transient frequency modulation spectroscopy as a function of argon pressure up to 0.2 atm at room temperature. Line shapes were fit using Fourier transforms of a parametrized time correlation function, including Doppler and velocity-dependent collisional broadening, and collisional shifts. Deviations from Voigt line shapes can be equally well fit by modeling the narrowing with a speed-dependent collision model or with a velocity-changing collisional narrowing model. Pressure broadening coefficients were observed with little rotational state dependence, in the range of 0.070-0.075 cm(-1) atm(-1). In contrast, stronger and qualitatively different rotational state dependences are observed for both pressure-dependent blue shift coefficients and the narrowing parameters. No asymmetry in the pressure broadened lines was observed.

Pure rotational spectra of the ground electronic-vibrational ${X}_{1}$ state of ${}^{204}$Pb${}^{19}$F, ${}^{206}$Pb${}^{19}$F, ${}^{207}$Pb${}^{19}$F, and ${}^{208}$Pb${}^{19}$F are measured with a resonator pulsed supersonic jet Fourier-transform microwave spectrometer. Also reported is a new measurement of the Stark effect on the optical spectra of $A\ensuremath{\leftarrow}{X}_{1}$ transitions. These spectra are combined with published high-resolution infrared spectra of ${X}_{2}\ensuremath{\leftrightarrow}{X}_{1}$ transitions in order to create a complete picture of the ground state of lead monofluoride. For the microwave data, molecules are prepared by laser ablation of lead target rods and stabilized in a supersonic jet of neon mixed with sulfur hexafluoride. For the optical Stark spectra, a continuous source of molecules is created in a nozzle heated to $1000{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}$C. The microwave spectra confirm, improve, and extend previously reported constants that describe the rotational, spin-orbit, and hyperfine interactions of the ground electronic state of the PbF molecule. A discrepancy concerning the sign of the hyperfine constant describing the ${}^{207}$Pb nucleus is discussed. Magnetic-field-dependent microwave spectra are used to characterize the Zeeman interaction in terms of two $g$ factors of the body-fixed electronic wave function. The optical Stark spectra are used to characterize the electric dipole moment of the ${X}_{1}$ and $A$ states.

Here we report precision microwave spectroscopy of pure rotational transitions of the {sup 207}Pb{sup 19}F isotopologue. We use these data to make predictions of the sensitivity of the molecule to P-odd, T-even and P-odd, T-odd effects.

A time-of-flight coincidence detector is demonstrated. This detector is optimized for use in a pseudocontinuous resonance enhanced multiphoton ionization scheme that requires photoelectrons and photoions to be detected in coincidence. The detector utilizes two simultaneously operating charged particle detectors, one for the detection of electrons and the other for the detection of ions. In order to allow for field reversal, the detectors are physically identical, differing only by the value of applied voltages. Particular attention is given to the implementation of a charge-to-voltage transducer that allows for subnanosecond detection of both electrons and ions.

We have measured the hyperfine energy level structure of the ${X}_{1}$ and $A$ states of $^{207}\mathrm{Pb}^{19}\mathrm{F}$ and found it to be in disagreement with previous predictions. Specifically, we find our data are reproduced by the hyperfine parameters ${A}_{\ensuremath{\perp},{X}_{1}}=7200\ifmmode\pm\else\textpm\fi{}150\phantom{\rule{0.3em}{0ex}}\mathrm{MHz}$, ${A}_{\ensuremath{\parallel},{X}_{1}}=10\phantom{\rule{0.2em}{0ex}}300\ifmmode\pm\else\textpm\fi{}800\phantom{\rule{0.3em}{0ex}}\mathrm{MHz}$, ${A}_{\ensuremath{\perp},A}=1200\ifmmode\pm\else\textpm\fi{}300\phantom{\rule{0.3em}{0ex}}\mathrm{MHz}$, and ${A}_{\ensuremath{\parallel},A}=3000\ifmmode\pm\else\textpm\fi{}2500\phantom{\rule{0.3em}{0ex}}\mathrm{MHz}$. The hyperfine structure may also be reproduced with ${A}_{\ensuremath{\perp},{X}_{1}}=\ensuremath{-}7200\ifmmode\pm\else\textpm\fi{}150\phantom{\rule{0.3em}{0ex}}\mathrm{MHz}$ and ${A}_{\ensuremath{\perp},A}=\ensuremath{-}1200\ifmmode\pm\else\textpm\fi{}300\phantom{\rule{0.3em}{0ex}}\mathrm{MHz}$. These negative hyperfine constants would, however, require a reinterpretation of the parity assignments of both the ${X}_{1}$ and $A$ states of the PbF molecule.

Doubly resonant multiphoton ionization of PbF has been achieved via the ${X}_{1}\ensuremath{\rightarrow}A$ and $A\ensuremath{\rightarrow}D$ transitions. Excitation of the $A$ to the $D$ state by narrow-bandwidth laser radiation is found to have a cross section of ${\ensuremath{\sigma}}_{D}=100\ifmmode\pm\else\textpm\fi{}30\text{ }\text{Mb}$. The ionization potential is found to be 7.55(1) eV, in agreement with our previous result. The lifetime of the $D$ state is found to be $250\ifmmode\pm\else\textpm\fi{}150\text{ }\text{ps}$ and the ionization cross section is found to be ${\ensuremath{\sigma}}_{+}=90\ifmmode\pm\else\textpm\fi{}60\text{ }\text{Mb}$. These characteristics allow for efficient state-selective ionization of the PbF molecule.

Resonance enhanced multiphoton ionization of the ${X}_{1}\phantom{\rule{0.2em}{0ex}}^{2}\ensuremath{\Pi}_{1∕2}$ state of lead monofluoride $(^{208}\mathrm{Pb}^{19}\mathrm{F})$ via the $B\phantom{\rule{0.2em}{0ex}}^{2}\ensuremath{\Sigma}_{1∕2}$ state is demonstrated. The ionization potential is observed to be $7.54(1)\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. Limits on the lifetime of the $B$ state are found to be consistent with that reported by Chen et al. The transition dipole moment for the ${X}_{1}\ensuremath{\rightarrow}B$ transition is found to be $0.005(1)\phantom{\rule{0.3em}{0ex}}\mathrm{a.u.}$ Limits on the ionization cross section of the $B$ state are found.

We present saturation absorption spectroscopy of transitions in Te2 near 444.4 nm. These spectra were taken using a blue diode laser locked to a Fabry–Perot (FP) cavity that is in turn locked to a Zeeman-stabilized helium–neon laser. Tuning of the diode laser frequency is accomplished by N2 pressure tuning of the FP cavity. The result is a tuning frequency that is proportional to the dispersion of the index of refraction between the helium neon and diode laser wavelengths. We assess the stability of the blue laser frequency by scanning over a single Te2 absorption line repeatedly over a 48 h period. This work is motivated by our desire to produce a versatile frequency-locked source of radiation for use in molecular optical polarization experiments.

A magnetic octupole filter set in a 90 degree sign curve produces {approx_equal}10{sup 8} cold Rb atoms/s by filtering low-velocity particles from a thermal source. We measure the speed distribution of Rb exiting the filter to be 3.5 K using a Rydberg-atom time-of-flight scheme in which Rb is excited via the process 5s {sup 2}S{sub 1/2}{yields}5p {sup 2}P{sub 3/2}{sup o}{yields}32d {sup 2}D. We develop a general theory of the transmission and speed distribution of particles emitted from such a source including nonadiabatic effects. A detailed Monte Carlo simulation using the theory accurately reproduces the experimental results. We show that for Cs, Li, and Rb atoms and S{sub 2} molecules, nonadiabatic effects do not dramatically effect the performance of the filter, and that the output flux temperatures for a wide variety of filter configurations are well fit to a simple functional form.