John L. Hardwick

Spectroscopy of the CH free radical

Abstract New emission observations of the A 2 Δ- X 2 Π and B 2 Π − - X 2 Π electronic transitions of the CH free radical were recorded. The A 2 Δ- X 2 Π and B 2 Σ − - X 2 Π data were obtained with a Fourier transform spectrometer and additional measurements of the A 2 Δ- X 2 Π transition were made with a spectrograph. These line positions were combined with the previous infrared vibration-rotation measurements in a simultaneous fit to determine the molecular parameters for the X 2 Π, A 2 Δ, and B 2 Σ − states.

Perturbations to the Cl2+A2Πu-X2Πg band system: Observation of a new electronic state

Abstract Fifteen emission bands of 35Cl2+ in the region between 415 and 490 nm have been recorded at high resolution in a supersonically cooled source and rotationally analyzed. All of these bands have Ω = 3 2 in both the upper and lower states. Among these, 10 bands are assigned to the principal A 2 Π u 3 2 -X 2 Π g 3 2 electronic band system first assigned rotationally by Huberman; these measurements substantially improve the accuracy with which vibrational intervals and rotational constants are known for this system. The remaining five bands are assigned to perturbation-induced transitions of a new band system whose most plausible assignment is B 2 Δ u 3 2 -X 2 Π g 3 2 . In addition, nine bands of 35Cl37Cl+, including one band belonging to the new B 2 Δ u 3 2 -X 2 Π g 3 2 system, have also been analyzed. These are the first reported rotational analyses of any bands of the minor isotope.

High-resolution studies of the A2Π-X2Π system of rotationally cooled SO+

Abstract Rotationally cold emission has been recorded for the A - X band system of SO + at high resolution using a slot-shaped corona excited supersonic expansion. Bands with v ′ = 0 up to 8 and v ″ = 3 up to 11 have been assigned and analyzed at high resolution using both cold spectra and spectra recorded using a higher temperature flowing afterglow. The derived parameters obtained from these spectra have been merged with those from previously published spectra of SO + to obtain substantially improved equilibrium constants and to calculate RKR turning points.

Λ-Doubling in the jet-cooled A-X emission spectrum of Cl2+

Abstract Several bands of the A - X emission spectrum of Cl 2 + have been recorded at high resolution in a rotationally cold supersonic expansion of Cl 2 and He excited with a corona discharge. Λ-type doubling has been observed for the first time in this system, confirming the identity of these bands as members of the Ω = 1 2 component of the electronic transition. Rotational constants have been obtained with higher precision than has previously been possible, allowing us to clarify some outstanding questions about the relative vibrational numbering of these bands.

Rotational and translational cooling of molecular ions produced in a slot nozzle

Excimer laser drilling has been used to cut a 20‐μm by 5‐mm slot in the end of a closed Pyrex tube. The slot nozzle thus formed is suitable for production of a corona‐excited supersonic expansion. The performance of the device has been characterized by recording the spectrum of the N+2B–X(0, 0) band at high resolution with the optical axis parallel to the slot and with the axis perpendicular to the slot (simulating a standard pinhole nozzle expansion) for comparison. The spectral lines recorded parallel to the slot nozzle are found to have a Doppler width such that a spin doubling of 0.06 cm−1 is resolved, while the pinhole‐type spectrum resolves spin doubling of 0.09 cm−1. The slot nozzle also enhances the intensity of the spectrum, reducing recording time from 10 to 2 min, while maintaining the same approximate rotational temperature of 20–40% K.

The vibration-rotation spectrum of the ν1 band of nitroxide, HNO−

Abstract The infrared spectrum of the nitroxide ion, HNO−, has been recorded in the region between 2940 and 3150 cm−1 using high-resolution autodetachment detection spectroscopy. This wave-number range corresponds to absorption near the ν1 vibration, the NH stretching mode. The rR4, rR5, rR6, rR7, rR8, rR9, and rQ6 branches have been identified and rotationally analyzed, and rotational and centrifugal distortion constants for the (0, 0, 0) and (1, 0, 0) states have been obtained. The principal rotational constants, in cm−1, are A″ = 15.233360(380); (B″ + C″) 2 = 1.096829(24) ; (B″ - C″) 2 = 0.034424(900) ; A′ = 16.937355(280); (B′ + C′) 2 =1.088597(22) ; and (B′ - C′) 2 = 0.036066(1600) . The ν1 band origin is 2750.7827 (53) cm−1.

Resonance-enhanced multiphoton ionization detection of a new 3Σ+-a3Π band system in CS

Abstract Resonance-enhanced multiphoton ionization has been used to detect absorption transitions from the nascent states of CS produced in the two-photon laser flash photolysis of CS2. Transitions are seen from the a3Π state of CS to a previously unobserved 3Σ+ state. Rotational assignments of the (1, 0), (0, 0), (0, 1), and (0, 2) bands have been made; the derived constants for those bands are similar to those of the CS+ ion, in good agreement with the assumption that the upper electronic state is the 3sσ3Σ+ Rydberg state.

Far infrared emission spectrum of the OH radical

Abstract The far infrared spectrum of a hydrogen-oxygen premixed flame has been observed in spontaneous emission between 50 and 375 cm−1 at a resolution of 0.15 cm−1 using a Fourier transform Michelson interferometer equipped with a liquid He-cooled bolometer. The spectrum consists of the pure rotational emission of H2O in its ground and vibrationally excited states and of OH in its ground state (X2Π, v = 0). Using the well-known dipole moments and rotational constants of OH and H2O, the relative abundance of these two molecules in the flame has been obtained directly from their relative emission intensity. The OH radical is present in an abundance approximately 5.5% that of H2O.

SO+ emission in a supersonic jet

Rotationally cold emission has been recorded in the A 2πi–X 2πr band system of SO+ at a resolution of 0.3 cm−1 using a source consisting of a supersonic expansion excited by a corona discharge. The observed spectra, including over 50 bands with v’=0–11 and v‘=0–10, have been rotationally analyzed and the derived constants have been merged with those obtained from previously published spectra.