The D2Σ+ – A2Πi and C2Πr – A2Πi transitions of AlO

Several bands of the D2Σ+ – A2Πi and C2Πr – A2Πi transitions of AlO have been photographed at high resolution and analyzed for the rotational structure. Rotational structure in the vibrational levels ν = 0, 1, 2, 3, and 4 of the common lower electronic state A2Πi has been investigated for the first time. Rotational perturbations have been observed in the A2Πi state. The equilibrium rotational constants of the A2Πi state are Be = 0.53705 cm−1 and αe = 0.00491 cm−1.

Absorption Spectrum of HSiI

A new absorption spectrum in the region 4600–5600 Å has been discovered in the flash photolysis of silyl iodide, SiH3I. A rotational analysis, together with the observation of a deuterium isotope shift, has shown that the spectrum is due to the HSiI radical.The lower electronic state of HSiI is a 1A′ state with a bond angle of ~103°, and the upper state is 1A″ with angle ~116°. Axis-switching effects, due to the increase in bond angle, cause the appearance of ΔK = 0, ± 2 subbands, in addition to the ordinary ΔK = ± 1 subbands.

The absorption spectrum of the free SiH2 radical

The absorption spectrum of SiH2 in the visible region has been photographed at high dispersion and the rotational structure of three bands has been analyzed. In the lower electronic state 1A1 the HSiH angle is 92° 5′ and the Si–H distance 1.516 Å, while in the upper state these parameters are 123° and 1.487 Å, respectively. The observed bands correspond to excitation of the bending vibration [Formula: see text] in the upper state. In the lower state, only one excited vibrational level, 010, has been observed, yielding [Formula: see text].

The spectrum and structure of singlet CH 2

The red absorption bands of CH 2 , previously shown to correspond to a transition between singlet states, have been analysed in detail. In the lower electronic state a 1 A 1 the molecule is a strongly asymmetric top with rotational constants A 000 = 20.14, B 000 = 11.16 and C 000 = 7.06 cm -1 . From these constants a CH distance of 1.11 A and an HCH angle of 102.4° is obtained. In the upper state b 1 B 1 the molecule is nearly linear, having an HCH angle of about 140° and a CH distance of 1.05 A. Most of the observed absorption bands correspond to excitation of the bending vibration v 2 in the upper state (v 2 = 6, 8, ..., 18). In some of them in addition the symmetric stretching vibration v 2 is singly excited. The levels 1, v 2 -4, 0 cause strong perturbations in the levels 0, v 2 , 0 for v 2 = 8, 10, 12, 14. In the lower state only one excited vibrational level 0, 1, 0 has been established which yields v 2 = 1352.6 cm -1. Fragments of some other singlet absorptions in the near ultraviolet and in the vacuum ultraviolet have been observed and are briefly described. The upper state of the near ultraviolet system is probably the predicted 1 A 1 state corresponding to 1 E + in the linear conformation.

THE SPECTRUM AND STRUCTURE OF THE HNO MOLECULE

The absorption spectrum of HNO in the region 6500–7700 Å has been photographed on a 35-ft grating. The observed spectrum consists of three bands: an intense one at the long-wavelength end of the spectrum and two weaker bands towards shorter wavelengths. All the bands have extensive rotational structure of the perpendicular type. The spectrum was observed after the flash photolysis of nitromethane, nitroethane, isoamyl nitrite, and mixtures of nitric oxide and ammonia. The "lifetime" of the HNO was about 1/10 second under our experimental conditions. The spectrum of DNO has also been photographed. From the constants obtained from the rotational analysis the molecular geometry has been determined. For the lower electronic state[Formula: see text]For the upper electronic state[Formula: see text]The most probable identification of the observed electronic transition is 1A″ ← 1A′.