Abstract

So far the internal states of molecules before and after the collisions with solid surfaces have been studied by using molecular beam techniques. However the number density of molecules in the molecular teams is not sufficient to monitor the population in each rotational levels with a reasonable signa1-to-noise ratio and a high resolution by means of the linear absorption spectroscopy. We have developed a novel laser spectroscopic method to prove the internal states of non-beam low density gas after collision with solid surfaces. A tunable diode laser (TDL) is used as a proving light source. The gas pressure is kept low enough (10⁻⁴ Torr), and then the mean free path of the molecular collisions is as long as several tens centimeters. Even at this pressure, the number density of molecules is by two or three orders of magnitude higher than that in molecular beams. By passing the laser beam just above the target surface, the scattered molecule is monitored before it collides with other molecules. The Stark modulation method with a transparent grating-type Stark electrode is used, to detect absorption signals. The absorption intensity due to the scattered molecules is obtained by subtracting a contribution of the incident molecules from the total signal.

© 1988 Optical Society of America