Stark coefficients for highly excited rovibrational states of H2O

Quantum beat spectroscopy is combined with triple-resonance vibrational overtone excitation to measure the Stark coefficients (SCs) of the water molecule for 28 rovibrational levels lying from 27,600 to 41,000 cm(-1). These data provide a stringent test for assessing the accuracy of the available potential energy surfaces (PESs) and dipole moment surfaces (DMSs) of this benchmark molecule in this energy region, which is inaccessible by direct absorption. SCs, calculated using the combination of a high accuracy, spectroscopically determined PES and a recent ab initio DMS, are within the 1% accuracy of available experimental data for levels below 25,000 cm(-1), and within 4.5% for coefficients associated with levels up to 35,000 cm(-1). However, the error in the computed coefficients is over 60% for the very high rovibrational states lying just below the lowest dissociation threshold, due, it seems, to lack of a high accuracy PES in this region. The comparative analysis suggests further steps, which may bring the theoretical predictions closer to the experimental accuracy.