Knowledge Bank

The fifth P-H stretching overtone bands of phosphine are currently investigated. The spectrum was recorded at room temperature with a gas pressure of 116 hPa between 12 500 and $12780cm-1$. The spectrometer is a titanium:sapphire ring laser (Coherent 899-29) pumped by an Innova 400, 15 W argon-ion laser, which is coupled to a high sensitivity acoustic cell ($\alpha min=5\times 10-9cm-1$) filled with gas. Most spectra were recorded with a laser power of 1.5 W, a time constant of 300 ms, and a typical sensitivity of $100-500\mu V$. The spectrum of phosphine has been recorded at room temperature with a gas pressure of 116 hPa between 12 500 and $12780cm-1$. The $\Delta v=6$ spectrum is characterized by one band system centered at $12678.2cm-1$. It is assigned to the local mode P-H stretching (600 $A1/E$) bands. The analysis started by locating the most intense and lines (with $K=J$) and the lines of the perpendicular band, using the ground state combination differences technique. The ground state constants were kept fixed to the values from the litterature (L. Fusina and G. Di Lonardo, J. Mol. Struct. 517-518 (2000) 67-78). Lines up to $J=0-6$ have been assigned. Last year a Hamiltonian model which makes use of simple arithmetic relations between some rovibrational parameters was used and a preliminary set of parameters was obtained. The molecular parameters seemed to confirm the local mode tendency of the $PH3$ molecule in the near infrared range. We are now attempting to reach the experimental accuracy. A $C3v$ model is used to take into account the vibration-rotation perturbations. This work is supported by the EU Commission (Research Training Network No. HPRN-CT-2000-00022).