N.P.C. Westwood

The photoelectron spectra of diazene, diazene‐d2, and trans‐methyldiazene

The photoelectron spectra of the transient species diazene, N2H2; diazene‐d2, N2D2; and trans‐methyldiazene, MeNNH have been recorded and interpreted. Four ionization potentials in the HeI energy range (21.2 eV) have been detected in the case of N2H2, where the orbital energies are found to follow the sequence n+, π, n−, and σ. N2H2 exhibits a highly structured photoelectron spectrum which has been fully resolved and analyzed in conjunction with its deutero analog. Several features of the spectrum are discussed, in particular the magnitude of the n+/n− separation, which is the largest yet observed, a comparison with N2F2 and the perfluoro effect, and the position of the π ionization. Our results also suggest that the 1700 A band in the absorption spectrum of N2H2 is a n+→3p Rydberg transition. In addition, using the experimental Franck–Condon factors, we have deduced the geometry of the N2H2 and N2D2 ground state ions and compared the photoelectron spectra with the isoelectronic molecules B2H6, C2H4, CH2N...

A versatile, fast pumping ultraviolet photoelectron spectrometer for the study of transient and unstable species

Abstract A high resolution ultraviolet photoelectron spectrometer specifically designed to study transient and unstable species is described. Its capabilities are enhanced by the novel pumping system for the analyzer, thus removing the necessity of a large vacuum chamber, and giving close access to the ionization chamber. Additional fast pumping for the ionization chamber and versatile sampling systems are also incorporated. Spectra are presented to show the general performance and the potential of the spectrometer for studying unusual chemical systems. In particular, the design features permit studies of discharge reactions, pyrolyses, atom-molecule reactions, highly reactive molecules and variable temperature work.

The microwave spectrum and structure of the unstable molecule bromine isocyanate, BRNCO

Abstract The microwave spectra of two isotopic species of the unstable molecule bromine isocyanate, BrNCO, have been observed from the flow reaction of Br 2 vapor with silver cyanate. The spectra were observed in the frequency range 8–54 GHz. They contain strong a -type transitions, as well as b -type transitions, with the latter so weak they initially could not be assigned. The transitions show Br and N quadrupole hyperfine structure; many perturbations in the former have been found, and have been used in a novel method to evaluate accurately all the rotational constants and the Br quadrupole coupling tensor entirely from a -type R branches. This has been done using a global least-squares fitting program developed especially for the purpose. The resulting constants permitted the b -type transitions to be identified. The molecule has been shown to be planar, the BrNCO configuration has been confirmed, and a partial r 0 structure has been determined. The principal values of the Br quadrupole tensor have been evaluated and the Brue5f8N bond has been shown not to be bent.

Photoelectron spectroscopic studies of some nitrosyl and nitryl halides and nitric acid

Abstract The He(I) photoelectron spectra of the compounds FNO, ClNO, BrNO, FNO 2 and ClNO 2 have been recorded on an instrument specifically designed to study reactive and short-lived species. The spectrum of HNO 3 (isoelectronic with the nitryl halides) is included for comparison. The spectra of the nitrosyl halides are interpreted by reference to SCF-MO calculations, by correlation with the known levels of NO, and by consideration of the electronic effect of the halide (X) substituent. The resulting assignments are in accord with weak bonding between the X and NO moieties. The assignments for the nitryl halides and nitric acid are assisted by correlation with the known levels of NO 2 , by consideration of the electronic effects of the X substituent, by an analysis of vibrational structure, and by CNDO type MO calculations. On the basis of our assignments for these latter molecules we propose a reassignment of the photoelectron spectrum of CH 3 NO 2 .

The infrared spectrum of gaseous aminoborane, H2NBH2: Location of the fundamentals and rotational structure in the 401 band (BN stretching vibration at 1337 cm−1)

Abstract The infrared spectrum of gaseous aminoborane, H2Nue5fbBH2, has been observed for the first time, following controlled thermal decomposition of NH3BH3 in a flow system. The positions of the nine vibrational fundamentals lying above 800 cm−1 have been determined from medium-resolution Fourier transform spectra, and the rotational structure of the ν4 fundamental (the BN stretching vibration at 1337.474 cm−1) has been studied at high resolution. The 41 level is extensively perturbed, and analysis of the perturbations has permitted the positions of the three lowest-lying fundamentals (which are either infrared inactive or below the wave number range of our spectrometer) to be estimated. An accurate set of rotational constants for the ground level of the molecule has been obtained.

Pyrolysis of trimethyl hexahydro-s-triazines. The photoelectron spectra of N-methylmethylenimine, CH2NCH3, and C-methylmethylen

Abstract The unstable methylated imines CH 2 ue5fbNCH 3 and CH 3 CHue5fbNH have been produced by low-pressure pyrolysis of the appropriate triazine

Thiocyanogen (SCN)2− preparation, ultraviolet photoelectron spectrum and structure

Abstract The unstable thiocyanogen molecule, (SCN) 2 , has been investigated in the gas phase by ultraviolet photoelection spectroscopy. Semi-empincal and ab intio calculations are used to assist with the orbital assignments and to provide an assessment of the structure A disulphide structure, with a dihedral angle of 87.8° is indicated, similar to those of other well known S 2 X 2 molecules.

The microwave spectrum of an unstable molecule: Chloroketene ClHCCO

The microwave spectra of four isotopic species of the unstable molecule chloroketene ClHCCO have been observed from the flow pyrolysis of monochloroacetyl chloride and from the pyrolytic reaction of dichloroacetyl chloride with zinc metal. The spectra, which consist only of b‐type transitions, were observed in the frequency range 26.5–80 GHz. Accurate rotational constants and quartic and sextic centrifugal distortion constants have been obtained for all isotopes. Large numbers of perturbations have been observed in the chlorine quadrupole hyperfine structure; consequently, the complete quadrupole coupling tensor has been evaluated. The dipole moment has been measured. The molecule has been shown to be planar, and a partial r0 structure has been determined.

Determination of rotational and centrifugal distortion constants using quadrupole hyperfine structure: The microwave spectrum of lodine isocyanate, INCO☆

Abstract The microwave spectrum of the unstable molecule iodine isocyanate, INCO, has been observed from the flow reaction of I 2 vapor with silver cyanate. The spectrum, which was measured in the frequency range 18–54 GHz, contains strong a -type and very weak b -type transitions. The transitions show I and N quadrupole hyperfine structure; many perturbations in the I structure have been observed. Our novel method for using such perturbations to evaluate otherwise unobtainable rotational constants has been extended to include centrifugal distortion constants. This has been done using a global least-squares fitting program developed especially for the purpose. The molecule has been shown to be planar, and a partial r 0 structure has been determined. The principal values of the I quadrupole tensor have been evaluated, and are consistent with a straight Iue5f8N bond.

The microwave spectrum of bromine isocyanate, Brnco: Determination of rotational constants from quadrupole hyperfine structure

Abstract A novel method has been developed to evaluate accurate rotational constants from the microwave spectrum of the unstable molecule bromine isocyanate, using perturbations in nuclear quadrupole hyperfine structure. It has been applied to this prolate near-symmetric rotor to determine A v and x ab accurately, entirely from a -type R branches. The method has been made possible by the development of a special computer program for global least-squares fitting to rotational and centrifugal distortion constants, along with all components of the Br nuclear quadrupole coupling tensor.