Infrared Laser Spectrum and Structure of Phosphoryl Chloride (ClPO) Formed at Ambient Temperature in the Gas Phase

Abstract

The infrared spectrum of the transient molecule phosphoryl chloride (ClPO) has been measured in the gas phase at room temperature using infrared diode laser absorption spectroscopy around 8 µm. The molecule was generated in a flow system either by adding molecular chlorine to a mixture of white phosphorus vapor and oxygen or by reacting atomic oxygen with phosphorus trichloride vapor. The infrared spectrum arises from the P-O stretching fundamental (ν 1 ) of ClPO. The band origin is determined as 1263.007 00(22) cm -1 , which is 5 cm -1 higher than the Ar matrix value and nearly 10 cm -1 lower than a recent low-resolution gas phase FTIR measurement. The rotational constants derived from the diode laser experiment, A ) 1.120, B ) 0.151429(29), and C ) 0.133 236(23) cm -1 , are very close to those calculated from the density functional theory (B3LYP) structure of R Cl-P ) 2.0958 Å, R P-O ) 1.4650 Å, and ∠Cl-P-O ) 110.07°.

Infrared Diode–Laser Spectroscopy of Phosphoryl Bromide (BrPO)

“…This shift is identical in magnitude and direction to that determined for ClPO (8) and is entirely reasonable in comparison with the blue shift in other P-O stretching frequencies. This value is 10 cm Ϫ1 lower than that determined by Boustani and Allaf from a low-resolution gas-phase FTIR spectrum (10).…”

“…The B and C rotational constants determined here are in good agreement with those calculated from the ab initio MP2 and DFT structures in Table 1. The DFT level of calculation has also proven remarkably successful for a number of similar phosphorus-containing triatomic molecules (8,12,13). The band origins are in reasonable agreement with the harmonic vibrational band origins found in the ab initio work, which predicts a very small isotopic dependence for this band in agreement with observations.…”

“…To constrain the ground state value of A, it was therefore necessary to assume that the inertial defect of BrPO was comparable to that of molecules of similar structure. As in the case of ClPO (8), an inertial defect of 0.15 a.m.u. Å 2 was chosen as a reasonable approximation in comparison to that of SSO and ClNO.…”

“…Our previous work on ClPO (8) found that the only readily assignable spectral features (the K a Q branches of an a-type band) were within 1 cm Ϫ1 of the band origin of the P-O stretch at 1263.007 cm Ϫ1 . Intensive searches were therefore made for the corresponding Q branches around the band origin of BrPO.…”

“…Recently, we used high-resolution infrared diode-laser spectroscopy to identify the ClPO molecule at room temperature for the first time spectroscopically (8). In the current paper, we describe the use of the same technique to identify another molecule in this series, namely BrPO.…”