MOLECULAR DEFORMATION OF B 1s CORE-EXCITED STATES OF BCl_3 
PROBED BY ANGLE-RESOLVED ION YIELD SPECTROSCOPY

Y. Shimizu$^\ast$, K. Ueda$^\ast$, H. Chiba$^\ast$, 
Y. Sato$^\ast$, M. Izumisawa$^\dagger$, T. Hayaishi$^\dagger$, 
M. Kitajima$^\ddagger$ and H. Tanaka$^\ddagger$

$^\ast$Research Institute for Scientific Measurements,
Tohoku University, Sendai 980-8577, Japan 
$^\dagger$Institute of Applied Physics,
University of Tsukuba, Tsukuba 305-8577, Japan 
$^\ddagger$Department of Physics, Sophia University,
Tokyo 102-8554, Japan 

We have measured the angle-resolved ion yield spectra in the 
vicinity of the B 1s -> 2a_2'' and B 1s -> 4e' resonances in 
the D_{3h} planar molecule BCl_3 and find that the B atom is 
pushed out in the B 1s^{-1}2a_2'' state while the molecule 
deforms mainly within the molecular plane in B 1s^{-1}4e'.