Observation of the visible absorption spectrum of H2O+

Abstract

The A 2 A 1 -X 2 B 1 system of H 2 0 + has been observed, using laser absorption spectroscopy in a velocity-modulated discharge. A total of78 transitions between 14 794 and 15 475 em_, have been observed with an uncertainty ( 1 SD) of 0.02 em-1 , including 76 transitions in the (0,7,0)-(0,0,0) band and 2 in the (0,8,0):-(0,0,0) band. This species is important for cometary astronomy, and intriguing for molecular physics because of its prominent Renner-Teller interaction. Careful measurements were made of the relative intensities of the absorption lines, which were measured to an accuracy of 13% (1 SD). This is the first observation of the A-X transition in absorption; all previous data were obtained in emission with conventional grating spectroscopy. The transition frequencies of our new data are in good agreement with previous work, and have improved accuracy. The new data have definite rejection of the interfering lines from excited neutral H 2 that plagued previous work. Compared with previous work, the new data have the first quantitative measurement of intensities. The ratio of the Franck-Condon factors / 8 / / 7 = 0.99 ± 0.43 has been measured for the first time, where I,,= FCF[ (O,v',0)-(0,0,0) ].

Vibronic transition moments and line intensities for H2O+

“…In addition to the work by Brommer et al [3] and Jungen et al [4], there is further experimental [7][8][9][10][11] and theoretical [12][13][14][15] literature on theà 2 A 1 and X 2 B 1 electronic states of H 2 O þ ; a review of these previous studies is given in the recent paper by Wu et al [16] which reports an observation, by means of optical heterodyne magnetic rotation enhanced velocity modulation spectroscopy, of the absorption spectrum of theà 2 A 1 -X 2 B 1 electronic transition of H 2 O þ in the region from 16 600 to 17 600 cm À1 . For a review of the theory of the Renner effect see pages 371-379 of [6], and Chapters 15 and 16 of [17]; a bibliography of papers on the subject is given in pages 411-412 of [6].…”

“…We have simulated the absorption spectrum of H 2 O þ in the wavenumber region from 14 800 to 15 400 cm À1 , and in Table 3 we compare the theoretical wavenumbers and intensities with the available experimental data [7,9] for the 100 strongest calculated lines with N 6 8 in this region. For 58 of the 100 lines in Table 3, experimental values for both transition wavenumber and transition intensity are available, and for these 58 lines we visualize the degree of agreement between theory and experiment in Fig.…”

“…b The number in parentheses is one standard error in units of the last quoted digits. Table 3 Calculated lower energies E 00 (in cm À1 ), calculated wavenumbers m (in cm À1 ), observed wavenumbers m obs (in cm À1 ) from [7], calculated line strengths S (in D 2 ), calculated intensities I calc (in km/mol), and observed intensities I obs (in arbitrary units) from [9] for the 100 strongest rovibronic transitions with N 6 8 of theà 2 A 1 -X 2 B 1 band system of H 2 O þ in the wavenumber region 14 800-15 400 cm À1 relative intensities found in the experiment were reproduced perfectly by the theoretical calculation, then each of the 58 lines would produce a point at (m obs À m calc ; I obs =I calc ) ¼ (0 cm À1 , 1). Many of the lines shown in Fig.…”

“…Further, line intensities Iðf iÞ were calculated from Eq. (56) of [15] at the absolute temperature T ¼ 500 K, which was determined as a reasonable value for a gaseous discharge by Das and Farley [9] in their observations of absorption lines in theà 2 A 1 ð0; 9; 0Þ X 2 B 1 ð0; 0; 0Þ andà 2 A 1 ð0; 10; 0Þ X 2 B 1 ð0; 0; 0Þ vibronic bands [which they incorrectly assigned as A 2 A 1 ð0; 7; 0Þ X 2 B 1 ð0; 0; 0Þ andà 2 A 1 ð0; 8; 0Þ…”

“…(35) of [15]) of individual rovibronic transitions involving theà 2 A 1 andX 2 B 1 electronic states of H 2 O þ have been computed with the RENNER program. The basis set employed (see, for example [23]) had (N 00 bend , 15,15,15,9,9,8,8). Further, line intensities Iðf iÞ were calculated from Eq.…”