Low-Temperature Rotational Relaxation of N2 Studied with Resonance-Enhanced Multiphoton Ionization

The rotational relaxation of molecular nitrogen has been investigated down to temperatures of about 5 K with a combination of resonance-enhanced multiphoton ionization and supersonic beam time-of-flight techniques. The average rotational relaxation cross section obtained shows a maximum value of 50-60 A2 at 20-30 K. For lower temperatures this cross section decreases and reaches a value smaller than 30 A2 at T ≈ 5 K. For temperatures above 30 K, the cross section decreases slowly as the temperature grows and converges approximately to the determinations from other non-jet techniques and theoretical estimates available for T > 80 K. The results are compared to previous measurements from other groups using different methods, and general good agreement is found. However, we observe a significant discrepancy with some of the data from electron-beam-induced fluorescence that yield much larger cross sections for temperatures lower than 30 K.© 1999 American Chemical Society
Program “Incorporación a Espan˜a de Doctores y Tecnólogos”of the Spanish Ministerio de Educación y Ciencia (MEC) and from the program “Ayuda a la Investigación” of the Fundación Caja de Madrid. Grants from the FPI program of the MEC. This work was financed by the MEC of Spain under DGICYT Project PB95/0918-C03.