Michael A. King

Microwave spectrum of the quasilinear molecule, cyanogen isothiocyanate (NCNCS)

Abstract The R-branch rotational spectrum of cyanogen isothiocyanate, NCNCS, produced by thermal isomerization of sulfur dicyanide, S(CN)2, has been measured between 26.5 and 40.0 GHz. The molecule shows archetypal quasilinear dynamic behavior in that the rotational satellite spectroscopic patterns for the low bending vibrational states, which lie below the barrier to linearity, are characteristic of a bent asymmetric top species and as vibrational excitation increases and states lie closer to or above the barrier the patterns gradually correlate with linear characteristic patterns. The spectrum, which consists of four transitions (J = 8 to 11), has been analyzed by treating the molecule as linear with one large amplitude, bending mode, ν7; the observed rotational constants were expanded in terms of the expectation values of even powers of the large-amplitude coordinate and various empirical constants determined. The inclusion of a small term in the vibrational Hamiltonian which accounts for the variation of reduced mass with bending coordinate has been found to be important. Relative intensity measurements indicate a barrier to linearity of 308 ± 34 cm−1 and a vibrational spacing (in the bent limit) of 97 ± 11 cm−1. The dipole moment, as determined from the ν7 = 3, l = 3 state, is 3.163(8) Debye.

Photoelectron spectra of the phospha-alkynes: 3,3-dimethyl-1-phosphabutyne ButCP and phenylphosphaethyne, PhCP

He(I) photoelectron spectra of the phospha-alkynes ButCP and PhCP have been obtained. The spectra have been assigned by comparison with spectra of related species and with the aid of ab initio SCF molecular orbital calculations. The first ionisation potentials are 9.61 and 8.68 eV for ButCP and PhCP respectively. These correspond to electron removal from orbitals with essentially π(CP) bonding character.

Ã2Σ+ → X̃+Π Emission spectra of the phosphaethyne cations, HCP+ and DCP+

Abstract The electron impact excited A 2 Σ + → X + Π emission spectra of HCP + and DCP + have been observed. The spin-orbit split 0-0 band has maxima at 593.7 and 599.0 nm for HCP + and 593.6 and 598.8 nm for DCP + . Short progressions in the V 3 (CP) vibration are observed. a 0 , v 3 and the upper-state lifetime are determined.

2Σ+ → 2Πi emission spectra of the phosphaethyne cations HCP+ and DCP+

Abstract Electron impact excited A 2Σ+ → X 2Πi emission spectra of HCP+ and DCP+ have been observed. The spectra consist of short progressions in ν″3. The 0 000 → 0 010 bands have been studied under high resolution and rotational analyses carried out. Some of the more important derived constants are (in cm−1) HCP+; ν″3 = 1150(10), A″0 = -146.97(3), B″0 = 0.6224(16), B′0 = 0.6690(17); DCP+; ν″3 = 1110(10), A″0 = -146.71(1), B″0 = 0.5284(2), B′0 = 0.5682(2).

à 2Σ+ → [Xtilde] 2Π i emission spectra of the thioborine cations HBS+ and DBS+

The emission spectra of the A 2Σ+ → [Xtilde] 2Π i transitions of HBS+ and DBS+ have been obtained by electron impact excitation. A vibronic analysis of the band systems has been made and the vibrational frequencies of the three modes in the [Xtilde] 2Π i state, and two in the A 2Σ+ state have been obtained for various isotopic derivatives. Renner and Fermi resonance effects of the bands involving the excitation of the ν2/″ mode have been considered and the parameters characterizing these interactions evaluated.

à 2Σ+ → [Xtilde] 2Π i emission spectra of the supersonically cooled cations HCP+ and DCP+

The emission spectra of the A 2Σ+ → [Xtilde] 2Π i electronic transition of rotationally cooled HCP+ and DCP+ cations have been obtained using electron impact excitation of seeded helium supersonic free jets. The resulting narrowing of the rotational envelopes enables weak transitions associated with single and double excitation of the degenerate v 2 bending mode in the [Xtilde] 2Π i state to be identified. The profiles of the bands are also used as a diagnostic tool in the assignments. The vibronic structure in the spectra, which is complicated by Renner and Fermi effects, has been analysed in terms of the parameters characterizing these interactions.

Laser‐excitation spectra of the chloroacetylene and deuterochloroacetylene cations, ClCCH+ and ClCCD+

The A 2Π←X 2Π laser‐excitation spectra of chloroacetylene and deuterochloroacetylene cations are reported. Analysis of the band systems yields values for all three stretching fundamentals (ν1–ν3) in the excited elecronic state. Rotationally resolved spectra of the 000Ω =3/2 subbands have been recorded and analyzed. The derived rotational constants allow estimates of the H–Cl distances in both electronic states to be made.

à 2Σ+ → X̃ 2Πi emission spectrum of the C‐fluorophosphaethyne cation FCP+

The A 2Σ+ → X 2Πi emission spectrum of FCP+ has been observed in the region 395–485 nm. The cations were produced by electron impact on an effusive beam of FCP molecules. Derived constants are (in cm−1): T0=24 077.7(0.6); A″0=−190.2(0.6) ν1″ =1729(2); ν3″=765(1); ν1′=1866(2); ν3′=817(2). The rotational structure indicates that B′≳B″.

The detection of unstable monomeric selenidoborons: chloroselenidoboron, C1BSE

High-temperature flow pyrolysis reactions carried out to detect unstable selenidoboron species, XB = Se (X = H or Hal) in the gas phase, have been successful in detecting the chloro-compound C1BSe which is the first in this family to be identified; characterisation by microwave spectroscopy indicates that r(BSe)= 1·751 ± 0·002 A.

Ā2A1 → X̄2E emission of 1-phosphapropyne cation, CH3CP+

The Ā2A1 → X2E emission spectrum of CH3CP+ in the gas phase has been observed in the 530–590 nm region. The cations were produced by electron impact on either an effusive beam or seeded helium supersonic free jet or CH3CP. Two pairs of spin-orbit separated bands are identified: O00, OOO and 2O1, 2O1. The derived constants are (in cm−1): T0=18656(1), a″O=−85(2) and ν″2=1503(2).