Ralph H. Page

Local modes of benzene and benzene dimer, studied by infrared–ultraviolet double resonance in a supersonic beam

We used rotational cooling of molecules to ∼5 K by supersonic expansion and state‐selective, multilevel saturation spectroscopy to obtain high‐resolution spectra of the fundamental and first and second overtone transitions of C–H stretching modes in ground‐electronic‐state benzene and its dimer. Greatly reduced linewidths (<3 cm−1 FWHM) in the rich spectra show that previously reported spectra have suffered from inhomogeneous congestion. Our observed spectral widths indicate that the vibrational lifetimes of the C–H stretches are at least a few ps, even at the energy of the second overtone (8800 cm−1). The ‘‘local mode’’ picture appears to apply when at least three quanta of C–H stretching motion are present. Spectra of the dimer are similar to those of the monomer but show a red shift of a few cm−1, the appearance of combination bands involving van der Waals vibrational modes, some intensity changes, and a broadening of spectral features that increases with the vibrational energy. The dimer’s predissocia...

Infrared–ultraviolet double resonance studies of benzene molecules in a supersonic beam

We have used IR excitation to selectively create populations in admixtures of the zeroth‐order states comprising the ∼3000 cm−1 ‘‘C–H stretching Fermi triad’’ of benzene. UV spectra of the 260 nm A(1B2u)←X(1A1g) transition in the IR‐excited molecules show several new bands, which we have assigned. Final states in the UV transitions are some vibrational levels which have not been detected before, allowing us to find several excited‐state vibrational frequencies. We have determined ν’3 =1327±3 cm−1, ν19 =1405±3 cm−1, and ν’20 =3084±5 cm−1. Also, vibrational structure which was unresolved in IR spectra of the ‘‘Fermi triad’’ was resolved in the UV double resonance spectra, confirming that the C–H stretching admixture is really a tetrad. The 3048, 3079, and 3101 cm−1 states had formerly been given the labels ν‘20, ν‘8+ν‘19, and ν‘1+ν‘6+ν‘19, respectively. Actually, the middle level most nearly resembles ν‘1+ν‘6+ν‘19, and the 3101 cm−1 level is strongly mixed with ν‘3+ν‘6+ν‘15. As predicted by molecular orbi...

Infrared predissociation spectra of water dimer in a supersonic molecular-beam

The infrared absorption spectrum of the hydrogen-bonded water dimer, (H2O)2, formed in a supersonic expansion, was recorded in the region of th

Frequency tripling into the 720–1025‐Å region with pulsed free jets

We have developed a coherent source of XUV light, which is continuously tunable between 904 and 1024 A, and line tunable to 720 A. It employs the technique of frequency tripling in a pulsed free jet of gas, and requires a single tunable laser system. Spectra of the relative XUV output vs wavelength in the 904–1024‐A range are presented for the tripling gases Ar, Kr, Xe, CO, and N2. Also listed are relative outputs obtained by tripling at resonantly enhanced lines between 720 and 900 A in Kr, Xe, and CO. Possible improvements to the source are discussed, and examples of its application are given.

High-resolution photoionization spectrum of water molecules in a supersonic beam

We have obtained high‐resolution (∼1.5 cm−1) photoionization spectra of supersonically cooled (Trot∼50 K) H2O and D2O in the 1000–900 A range. The light source, which used the technique of frequency tripling in a pulsed free jet of gas, is described briefly. Spectra are rotationally resolved. Vibrationally excited autoionizing Rydberg series converging to the ground electronic [X; (1b1)−1] state of the molecular ion are detected. This may well be the first example of a highly resolved Rydberg spectrum of a stable polyatomic molecule. From the convergence limit, the ionization potential H2O is determined to be 101 777±7 cm−1. Intensities of the Rydberg state autoionization signals are smaller than predicted with known Franck–Condon factors, indicating that predissociation is a competitive decay channel. Rydberg state lifetimes are ∼1 ps, deduced from homogeneous linewidths. Autoionizing features from Rydberg states associated with the ion’s quasilinear A (3a1)−1 state are observed with linewidths above 1...

RYDBERG SPECTROSCOPY OF H2 VIA STEPWISE RESONANT TWO-PHOTON ION-PAIR (H++H-) PRODUCTION

High-resolution spectra of new Rydberg states of H/sub 2/ in the extreme uv region were obtained by two-step doubly resonant excitation followed by H/sup -/-ion detection. Resolved Fano-line profiles showing a sign reversal of the profile index along the Rydberg series were observed for the first time in H/sub 2/. Dynamical information such as lifetimes and relative transition strengths was also derived.

Rydberg spectroscopy of H/sub 2/ via stepwise resonant two-photon ion-pair (H/sup +/+H/sup -/) production

High-resolution spectra of new Rydberg states of H/sub 2/ in the extreme uv region were obtained by two-step doubly resonant excitation followed by H/sup -/-ion detection. Resolved Fano-line profiles showing a sign reversal of the profile index along the Rydberg series were observed for the first time in H/sub 2/. Dynamical information such as lifetimes and relative transition strengths was also derived.

Infrared vibrational predissociation spectra of large water clusters

Abstract The infrared absorption spectrum in the OH stretching region of (H2O)19 clusters formed in a supersonic molecular beam is reported. It was obtained with mass-spectrometric detection and is compared with a similarly obtained spectrum of (H2O)6 and a large-cluster spectrum obtained with bolometric detection. The mass-resolved spectra show a broad absorption band between ≈ 3200 and 3600 cm−1, reminiscent of the H-bonding feature in acondensed phase spectrum. The spectrum via the bolometer is peaked to the blue of this region, suggesting that the level of H-bondingis much lower. Mass resolution is clearly advantageous in selectively obtaining spectra of large clusters, free of interferencefrom smaller ones.

Demonstrations of diode-pumped and grating-tuned ZnSe:Cr{sup 2+} lasers

A diode-side-pumped ZnSe:Cr{sup 2+} laser was operated with a 75 - Watt peak power 1.65 {micro}m InGaAsP/InP pump array. The laser was configured with a ``single-bounce`` architecture to maximize its round-trip gain. Peak output powers of {approx}0.3 Watt were obtained with a 10% - transmitting output coupler and a lightly-doped crystal. The estimated ``mode fill`` of {approx}0.06 will increase with Cr{sup 2+} concentration, raising the output power and extraction efficiency. With a grating tuner and MgF{sub 2}:Co{sup 2+} laser pumping, the laser tuned throughout the 2134 - 2799 nm range.

1-watt composite-slab Er:YAG laser

A diode-side-pumped discrete-optic Er3+ :YAG laser employs pump-light coupling through a sapphire plate diffusion-bonded to the laser slab, removing heat directly at the pump face of the slab instead of requiring conduction through to its far side. This lowers the temperature in the gain region and gives reduced thermal lensing, which produces exceptional beam quality (M2~ 1.3) at output powers -0.3 Watt. Powers above 1 Watt have been demonstrated with peak slope efficiencies ~20%. The novel architecture is also applicable to other side-pumped lasers.