Peter A. Hamilton

Photobleaching of 5,10,15,20-tetrakis(m-hydroxyphenyl)porphyrin (m-THPP) and the corresponding chlorin (m-THPC) and bacteriochlorin(m-THPBC). A comparative study

Abstract The photobleaching of compounds of the 5,10,15,20-tetrakis(m-hydroxyphenyl)porphyrin series at different reduction levels (m-THPP 1, m-THPC 2, m-THPBC 3) has been studied in methanol and in methanol–water (3:2, v/v) using an argon laser (514 nm) by observing the diminution of absorbance of band I (for 2 and 3) and of band IV (for 1) with time. Under the conditions studied here, true photobleaching only occurs for m-THPC (2) and m-THPBC (3), with photomodification being the major process for m-THPP (1). The rates for the photobleaching of 2 and 3 are presented in different solvents. The photobleaching rate of the bacteriochlorin 3 is found to be 90 times higher than that of the chlorin 2 in methanol–water (3:2, v/v). Singlet oxygen appears to be the reactive species responsible for the photobleaching of 2 and 3 and the photomodification of 1.

Infrared laser spectroscopy of the ν3 fundamental of HCO

Eighteen lines in the P and R branches of the ν3 band of HCO+ have been measured by diode‐laser absorption spectroscopy using a velocity modulation technique. The position of the band center is 2183.9505(51) cm−1.

Observation of ArOH in a pulsed discharge system

Abstract The free-radical complex ArOH has been generated in a pulsed electric discharge in a supersonic free-jet expansion of argon and water vapour. Both OH and ArOH are found to be rotationally cold but vibrationally excited OH was also observed. The laser-induced fluorescence excitation spectrum of the complex is similar to that reported by other workers but shows a series of satellite bands to the red of the main progression which have no discernable rotational structure at Doppler-limited resolution. As these bands increase in intensity as the effective temperature of the complex is raised, they are tentatively assigned to transitions arising from vibrationally excited van der Waals levels in the ground state.

Infrared laser spectroscopy of H 3 O + between 510 and 1150 cm −1

Lead-salt-diode lasers have been used to detect more than 100 absorption lines of H3O+ in an ac discharge by using the velocity-modulation technique. Many lines have been assigned to vibration–rotation transitions in the 1− ← 0+ and 1+ ← 0− components of the ν2 inversion mode of H3O+ with band centers at 954.4 and 525.8 cm−1, respectively. The results for the former band extend those of earlier work and lead to some minor changes in assignment.

Infrared diode laser spectroscopy of the ν2(2+ ← 1−) band of H3O+

Abstract Rotational lines in the ν2 = 2+ ← 1− “hot” band of the inversion mode of the oxonium (H3O+) ion have been recorded by diode laser absorption spectroscopy. The ion was generated in low pressure gas discharges and detected using both velocity modulation and modulated hollow cathode techniques. Analysis of the spectra using a simple oblate symmetric top model has allowed the rotational parameters describing the 2+ inversion state to be determined for the first time. The band origin lies at 521.4383(52) cm−1. These data will be useful in refining the oxonium ion inversion potential function and should aid in the analysis of other bands involving or perturbed by the 2+ level.

Stratospheric HBr concentration profile obtained from far-infrared emission spectroscopy

Hydrogen bromide (HBr) is the principal bromine sink species for the ozone loss chemistry induced by bromine‐containing gases in the stratosphere. We report a 1994 balloon‐based measurement of the daytime stratospheric HBr profile between 20 and 36.5 km altitude. The average concentration result of 1.31±0.39 parts per trillion in volume (pptv) and an analysis for the concentration versus altitude profile are consistent with previously reported measurements. These results strengthen the evidence for a significantly higher HBr concentration than that predicted by current photochemical models which, on the basis of recent kinetics results, do not include significant HBr production by the reaction branch, BrO + HO2 → HBr + O3.

Fourier transform spectroscopy of the ν1 and ν3 fundamental bands of CF2

Abstract The ν 1 and ν 3 fundamental bands in the ground electronic state of the transient CF 2 molecule have been measured using a high-resolution Fourier transform spectrometer. The spectra were recorded at 0.004 cm −1 resolution and over 1000 transitions in the ν 1 band covering K a values up to 15 and J values up to 40 have been analyzed. The ν 3 -band analysis included 860 transitions covering K a values up to 13 and J values up to 44. The rms deviation of the fits were 0.00027 cm −1 for ν 1 and 0.00025 cm −1 for ν 3 . Inclusion of the Coriolis coupling between the ν 1 and ν 3 bands improved the rms deviation to 0.00020 cm −1 and leads to a complete set of deperturbed constants. The analysis yields ν 0 ( ν 1 ) = 1225.08434(9) cm −1 , ν 0 ( ν 3 ) = 1114.44262(9) cm −1 , and rotational constants which are improved over those obtained in previous diode laser studies.

A hot band LIF study of the A 1Πu-X1Σ+g transition in C3

Abstract Laser-induced fluorescence excitation spectra of the A 1 Π u -X 1 Σ + g electronic transition have been recorded in the laser wavelength range 386–463 nm using a novel source of rotationally cold but vibrationally excited C 3 . A large number of new transitions are observed and we report here on some prominent vibrational progressions appearing in the spectra which are assigned to ( n ′ 00- n ″ 00) vibronic transitions. A tentative assignment of the (001-001) transition is also given which locates for the first time the A 1 Π u (001) level.

FIRST-SPIRE spectrometer: a novel imaging FTS for the submillimeter

The SPIRE instrument for the FIRST mission will consist of a three band imaging submillimeter photometer and a two band imaging Fourier Transform Spectrometer (FTS) optimized for the 200 - 400 micrometers range, and with extended coverage out to 670 micrometers . The FTS will be used for follow-up spectroscopic studies of objects detected in photometric surveys by SPIRE and other facilities, and to perform medium resolving power (R approximately 500 at 250 micrometers ) imaging spectroscopy on galactic and nearby extra-galactic sources.

The laser induced fluorescence spectrum and radiative lifetime of PO2

The ultraviolet spectrum of PO2 first observed in absorption by Verma and McCarthy has been studied by laser induced fluorescence for the first time. The spectra are similar in many respects to those observed in the visible system of NO2 and no predissociation is observed. The loss of rotational structure is attributed instead to mixing with one or more near continuous ‘‘background’’ states, with the amount of mixing apparently related to excitation of the bending vibration. The radiative decays are observed to be nonexponential but are accurately described by a double exponential form. This gives collision free radiative lifetimes of about 0.5 and 4.5 μs for the structured and continuous states, respectively, with the effective lifetime of the structured state varying strongly with the amount of mixing. Collisional quenching rate constants are roughly constant at (6±1)×10−10 and (4±1)×10−11 cm3 molecule−1 s−1 for the two states, with the very rapid quenching rate of the structured state probably being fo...